All Abrahamic religions believe in the return of the savior, the liberator of the human beings and redeemer, in the End-Time. Prophets and divine messengers have promised the day that the whole universe will be full of justice and tenderness. Other religions also have similar beliefs, although they differ in some minor aspects, which will be discussed below. We go through references from different religions and faiths to examine their views about the last savior. 

Kalki: The Last Savior in Hinduism

In Upanishads, which is a collection of ancient Sanskrit texts that contain some of the central philosophical concepts and ideas of Hinduism, the last savior is called Kalki. He is believed to be the tenth avatar of Hindu god Vishnu in the last of the four stages in the endless cycle of existence known as "Samsara," which is defined "as the endless cycle of birth, death, and rebirth. Or as the world of suffering and dissatisfaction (dukkha)" [1].  He rides a white horse with a fiery sword. He will end the darkest and destructive period to remove adharma [i] and will usher in the Satya Yuga [ii][2]. 

Another reference talks about a just commander at the end-time who is the leader of angels and humans, who knows the truth and gets hold of everything from deep in the seas too high in the mountains, and no one greater than him will come to earth [3].

Saoshyant: The Eschatological Savior in Zoroastrianism

In Zoroastrianism, there are three saviors who each will rise in a thousand years. The last one is an eschatological savior figure who will destroy evil and will bring about the renovation of the world. He is called Saoshyant, which means the beneficent in its single form. Yet, in its plural form, it is considered to mean the redeemer. The Khorda Avesta describes this savior as such:

Whose name will be the victorious SAOSHYANT and whose name will be Astvat-ereta. He will be SAOSHYANT (the Beneficent One) because he will benefit the whole bodily world; he will be ASTVAT-ERETA (he who makes the bodily creatures rise up), because as a bodily creature and as a living creature he will stand against the destruction of the bodily creatures, to withstand the Druj of the two-footed brood, to withstand the evil done by the faithful. [4]
Accordingly, the Soashyant will rise at the end-time and fight against the vices in the world and spread justice and goodness far and wide. 

Maitreya: The Future Buddha

In some of the Buddhist references, such as the Amitabha Sutra and the Lotus Sutra, we read about the future Buddha of this world, called Maitreya, who will be a successor to the present Buddha. In Sanskrit, Maitreya means kindness and love. According to Buddhist religious texts, Maitreya will be the fifth and last Buddha who will appear on the earth. The arrival of Maitreya is expected at a time in the future when the dharma will have been forgotten by most on the earth. That is when Maitreya will appear on the earth to achieve complete enlightenment and to teach the pure dharma [5].

Li Hong: The Last Savior in Taoism

The Taoist last savior, called Li Hong, is depicted as an ideal leader who would reappear to set right heaven (tian) and earth (dì) at a time of upheaval and chaos. Li Hong will appear at the end of the world cycle to rescue the chosen people, who would be distinguished by certain talismans, practices, and virtues [6].

Savior in Abrahamic Religions

Moshiach: The Last Savior in Judaism

The Jews belief in the savior is manifested in the idea of the coming of Moshiach (i.e., Messiah). This person is believed to be a descendant of King David, who will "gather the Jews from all over the world and bring them back to the land of Israel" [7]. There are many verses in different scriptures and Talmudic [iii] literature which refer to this figure and enumerate his characteristics and manners [iv]. For instance, Isaiah says:

And there shall come forth a rod from the stock of Jesse [King David's father], and a branch shall grow from his roots; and the spirit of the Lord shall rest upon him, the spirit of wisdom and understanding, the spirit of counsel and might, the spirit of knowledge and of the fear of the Lord. And his delight shall be in fear of the Lord; and he shall not judge by what his eyes see, nor decide by what his ears hear. But with righteousness shall he judge the poor, and decide with equity for the humble of the earth; and he shall strike the earth with the rod of his mouth, and with the breath of his lips shall he slay the wicked.
–Isaiah 11:1-4

Those who follow Judaism believe that their savior has not been born yet. Therefore, they are eagerly awaiting the coming of the one who will save them and establish a just dominion in which "there will be world peace, no more wars nor famine, and, in general, a high standard of living" [7]. 

The Messiah: Jesus Christ (PBUH) the Savior of Mankind 

Christians believe that Jesus Christ (PBUH) is himself the savior of humankind, and he was born for this purpose. The name Christ literally means "the anointed one" or the Messiah [8]. As the Gospel of Matthew says, Jesus Christ (PBUH) has been sent to "Save his people from their sins" (1:20-21). It is also believed that Jesus Christ (PBUH) had been crucified to atone the sins of humanity and lead them toward salvation. According to Christian sources, Jesus Christ (PBUH) was the savior who was awaited by the Jews as whose coming was predicted in the Torah as the Moshiach. 

Another point which makes Jesus Christ (PBUH) the awaited savior in Christianity is the idea of his second coming or the Second Advent in the end-time to whose "day or hour no one knows, not even the angels in heaven, nor the Son, but only the Father" (Mark 13:32). This is the belief in "the future return of Christ in glory when it is understood that he will set up his kingdom, judge his enemies, and reward the faithful, living and dead" [9]. Different gospels, including Matthew chapters 24–25; Mark, chapter 13; Luke, chapter 21:5–26, and John, chapter 14:25–29, are mentioned as the evidence for this belief. Moreover, according to biblical verses, there will be many signs indicating the end-time among which the second coming of Jesus Christ (PBUH) and the last judgment. 

Therefore, like many other religions, Christians also believe in a savior or as they call it the Messiah, who will make this world a better place and free it from oppression and injustice. 

Imam Mahdi (AS): The Awaited Savior in Islam

In Islam, the belief in the savior is rooted in the fact that Allah never leaves His creatures, especially human beings, on their own and support them through sending His apostles to guide them toward the right path: "and there is a guide for every people" Quran (13:7). He had sent 124000 prophets (PBUT) first, followed by righteous leaders who continued the path of previously chosen messengers of Allah. As the Quran says, "Certainly We wrote in the Psalms, after the Torah: 'Indeed My righteous servants shall inherit the earth.'" (21:105).

 Therefore, the earth will never become empty of Allah's guide, and people will benefit from these guiding lights either directly or indirectly. Imam Mahdi (AS), the twelfth leader of Muslims and a descendant of Prophet Muhammad (PBUH&HP), who is leading a secret life at the time, will ultimately rise and spread peace and humanity throughout the earth. "The Holy Prophet (PBUH&HP) informed Muslims about his reappearance, telling his names, attributes, appellations, and peculiarities" [10]. The time of his coming is unknown, and it is followed by the preparation of particular circumstances. 

The signs that indicate his coming include "Widespread injustice and oppression, the advent of Dajjal (Anti-Christ) who would misguide the thinking of the people, the advent of Sufyani who is one of the pillars of mischief and corruption on the earth, the formation of the Islamic army, which would raise up black standards, the voice of the angel of the sky giving glad-tidings of his reappearance, the coming down on earth of Jesus Christ (PBUH) and his paying allegiance to and praying behind in congregation Prayers led by Imam Mahdi (AS)" [11]

This belief in the last savior, who would stand against tyranny and injustice and remind human beings of their real value, also, highlights Islam's optimism toward the future of the world.

Finally, we have reviewed the belief in the last savior or the person who will save humankind from the evilness and destruction in this world in different faiths and religions. On a more in-depth look, we can find many similarities between these beliefs. However, the Abrahamic religions had a more precise and more tangible attitude toward the idea of the last savior and the time of his coming. Therefore, the concept of the savior is one of the most essential and significant matters regarding the future of human destiny. 

Notes:
[i] Opposite to dharma, which includes unnaturalness, wrongness, evil, immorality, wickedness, and vice. 
[ii] The period when humanity will be governed by gods and every manifestation or work is close to the purest ideal, and humanity will allow intrinsic goodness to rule supreme.
[iii] The central text of Judaism and the primary source of the Jewish religion. 
[iv] Isaiah 2, 11, 42; 59:20, Jeremiah 23, 30, 33; 48:47; 49:39, Ezekiel 38:16, Hosea 3:4-3:5, Micah 4, Zephaniah 3:9, Zechariah 14:9, Daniel 10:14. 

References:

1. Samsara
2. the man on the white horse
3. The Vishnu Purana, trans. Horace Hayman Wilson, London: Trübner & co., Book IV, Chapter 24.
4. Khorda Avesta, Translated by James Darmesteter (From Sacred Books of the East, American Edition, 1898.), Part five
5. Buddhism
6. Anna K. Seidel. "Perfect Ruler in Early Taoist Messianism: Lao-tzu and Li Hung." History of Religions, Vol. 9, No. 2/3
7. The end of days
8. what does christ mean
9. second coming
10. Sayyid Ali al-Husayni al-Milani, The Promised Savior: An inquiry into the imamate of Imam Mahdi (as) from the viewpoint of Muslim thinkers, part 1, p.8. 
11. Baqir Shareef al-Qurashi, The Life of Imam al-Mahdi, Trans. Sayyid Athar Husayn S.H. Rizvi, p.259-283. Pdf. 

There is a question that occupies the minds of many of us; what will remain of us in this world after we are long gone? Have we left this world and the generations followed by us a worthy legacy? Or we will soon be forgotten? Or even worse, we have left so much evilness and destruction that would never be wiped away from the face of this world? Looking at the lives of prominent figures, throughout the history of Islam, we realize how much effort they have put into spreading a valuable message and leaving behind an enduring legacy for future generations. Despite being under the restraint and pressure of the Caliphs of his time, Imam Sadiq (AS), the sixth Imam of Shias and one of Prophet Muhammad's (PBUH&HP) grandchildren, has left Muslims with the most considerable amount of religious content which turned into an essential point of reference for them until the present.

In what follows, we will have a look at the life of Imam Sadiq (AS), this praised personality. 

Birth and Lineage

Ja'far b. Muhammad b. 'Ali b. al-Husayn b. 'Ali b. Abi Talib (AS), known as Imam Sadiq (AS), was born on April 20, 702, in Medina. His father was Imam Muhammad al-Baqir (AS), and his mother was Umm Farwa, the daughter of al-Qasim, son of Muhammad b. Abi Bakr [1]. He had the opportunity to spend twelve years of his life with his grandfather, Imam Sajjad (AS), and thirty-one years with his father. His title al-Sadiq, which literally means "truthful," was given to him, since he avoided any direct involvement in the uprisings of his time [2]. 

Imam Sadiq (AS) had ten children, among whom was Imam Musa al-Kazim (AS), who was born on 745 A.D. 

Imam Sadiq (AS) 's Life at the time of Umayyad's Caliphate 

After the martyrdom of Imam Baqir (AS), Imam Sadiq (AS) was chosen as the leader of Shia Muslims, which lasted thirty-four years. The period of Imam Sadiq (AS) 's leadership coincided with the reign of the last five Umayyad caliphs, including Hisham b. 'Abd al-Malik, Valid b. Yazid b. 'Abd al-Malik, Yazid b. Valid b. 'Abd al-Malik, Ibrahim b. Valid b. 'Abd al-Malik and Marwan b. Muhammad.

 While Imam Sadiq (AS) witnessed a period of hardship and restrain under the reign of Hisham, after some years due to the weakening of Umayyads, which finally led to the fall of this dynasty, he found the chance to engage in scholarly activities and promote the actual Islamic teachings. He held many secret gatherings and meetings in which up to four thousand people attended, Imam Sadiq (AS) transferred his knowledge to his students, which later quoted many Hadiths from him and turned into authentic sources for future Muslim scholars [3]. 

Imam Sadiq (AS) 's Leadership at the time of Abbasid's Caliphate

After the fall of the Umayyad dynasty, Imam Sadiq (AS) witnessed the rise of Abbasid caliphs and lived during the reign of two of them, including al-Saffah and al-Mansur al-Dawaniqi. During the time of the first Abbasid caliph, al-Saffah, which was a period of instability and social and political upheavals, being engaged mostly in abolishing the remaining of Umayyad dynasty and their followers, provided Imam Sadiq (AS) with an excellent chance to go on with his scholarly and religious efforts and attract as many students as he could. 

Nevertheless, with the coming of al-Mansur to the throne, a period of total suppression and severe restraint began. During his realm, people lived in utter terror, and any kind of opposition was punished severely. Therefore, al-Mansur considered Imam Sadiq (AS) and his followers as a threat to his throne, and since Imam Sadiq (AS) was a public figure respected by all the people, he couldn't hurt him directly. So, he tried to weaken Imam's (AS) reputation and social status by enticing his students to engage in a debate with Imam Sadiq (AS) and defeat him. But all their efforts were futile [4]. 

Al-Mansur made many attempts to bring harm to Imam Sadiq (AS) and summoned him a few times to his court, intending to assassinate him, yet he wasn't successful. Imam Sadiq (AS) generally didn't tend to meet al-Mansur and attend his court. Al-Mansur was offended by Imam Sadiq's (AS) manner and one day asked him, "Why don't you come to meet me in my court like others?" and Imam (AS) answered, "I didn't do anything to be afraid of you, and you don't benefit us in the hereafter so that I would have hope in you. This position of you is not a blessing to be congratulated by me, and you don't find it a disaster to be comforted by me. So why would I attend you?" [5]   

Fighting against Deviatory Movements 

During Imam Sadiq's (AS) life, some religious groups formed, which deviated from the true teachings of Islam and Prophet Muhammad's (PBUH&HP) tradition. To oppose these movements and save Islam from such deviations, Imam Sadiq (AS) held many debates with the heads of these groups and tried to bring their falsehood into the light. Or he would send his students to have discussions with them. He always advised his students and followers to be wary of such deviatory movements and cut all ties with them. 

Scholarly and Scientific Movement 

As it was mentioned above, Imam Sadiq (AS) enjoyed an excellent opportunity to spread his knowledge among as many people as he could, which resulted in the transmission of a significant number of hadiths from him to the future generation. Therefore, most of the hadiths in fiqh or theology are from Imam Sadiq (AS) [2]. Due to his significant role in spreading the true Islamic teachings, Twelver Shiism is often called Ja'fari School [3]. Moreover, he held many dialogues and debates with theologians and scholars of different sects and religions, and even atheists, in which he managed to prove the authenticity of his stance. Some of the most famous students of Imam al-Sadiq (a) are Zurara b. A'yan, Burayd b. Mu'awiya, Jamil b. Darraj, 'Abd Allah b. Muskan, 'Abd Allah b. Bukayr, Hammad b. 'Uthman, Hammad b. 'Isa, Aban b. 'Uthman, 'Abd Allah b. Sinan, Abu Basir, Hisham b. Salim, Hisham b. al-Hakam. 

Prominent Moral Characteristics

Imam Sadiq was famous for his piety, knowledge, abundant and devoted worship, and great generosity [7]. It is reported that he spent a significant part of his time praying, fasting, or saying dhikr (remembrance) [8].  

Many narrations are reported about his generosity and kind manner toward people who lived in poverty. For instance, "it is reported that the Imam (AS) gave four hundred dirhams to a beggar, and when he thanked the Imam (a), he (a) gave him his ring, which was worth 10,000 dirhams. According to another report, the Imam would put some bread, meat, and money in a bag and would take it to the houses of the poor and divide it among them, without letting them know who he was. Abu Ja'far al-Khath'ami reports that Imam al-Sadiq (a) gave him a bag of money and asked him to give it to someone from Banu Hashim without telling him from where the money was coming. When Abu Ja'far gave the money to that man, he prayed for the sender and told him that this person always sends him money, but Imam al-Sadiq (a) never sends him anything even though he is rich!" [9] 

Martyrdom

Imam Sadiq (AS) was martyred on 765 A.D. at the age of sixty-three, poisoned by order of al-Mansur al-Dawaniqi. He was buried in the al-Baqi' Cemetery beside his father, Imam Baqir (AS), his grandfather Imam Sajjad (AS), and his uncle Imam Hasan (AS) [10].   
  

References:

1. Mufīd, Muḥammad b. Muḥammad al-. Al-Irshād fī maʿrifat ḥujaj Allāh ʿalā l-ʿibād. Vol.2, P.180.  
2. Pākatchī, Aḥmad. 1389 Sh. "Imām Jaʿfar Ṣādiq (a)". Dāʾirat al-Maʿārif-i Buzurg-i Islāmī 18:180-220. 
3.  Shahīdī, Sayyid Jaʿfar. Zindigānī-yi Imām Ṣādiq Jaʿfar b. Muḥammad (a), p. 47. 
4. Al-Suyuti, History of the Caliphs, p. 208-209. 
5. Baha' al-Din 'Ali b. 'Isa al-Irbili, Kashf al-ghumma fi ma'rifat al-a'imma, vol.2, p.208.  
6. Kulaynī, Muḥammad b. Yaʿqūb al-. Al-Kāfī. vol. 1, p. 79, 80, 171-173. 
7.  Baha' al-Din 'Ali b. 'Isa al-Irbili, Kashf al-ghumma fi ma'rifat al-a'imma, vol.2, p.691. 
8.  Majlisī, Muḥammad Bāqir, Biḥār al-anwār, vol. 47, p. 16.
9. Imam sadiq
10. Ibn Shahrāshūb, Manāqib Āl Abī Ṭālib, vol. 4, p. 210.