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 no doubt among us that after our dear Prophet Mohammad (PBUH&HP), our twelve Imams (AS) are the most important figures of our religion. On that account, today we want to get to know more about our first imam and the first male convert of the religion birth matter and conditions.

The faithless say, ‘You have not been sent [by Allah].’ Say, ‘Allah suffices as a witness between me and you, and he who possesses the knowledge of the Book’
The Holy Quran (13:43)

And among the people is he who sells his soul seeking the pleasure of Allah, and Allah is most kind to [His] servants
The Holy Quran (2:207)

If the two of you repent to Allah... for your hearts have certainly swerved, and if you back each other against him, then [know that] Allah is indeed his guardian, and his supporters are Gabriel, the righteous among the faithful and, thereafter, the angels...
The Holy Quran (66:4)

If we seek the true meaning of these three verses above of our holy book, they all seek Ali (AS) as their primary target and guide us to some aspects of his life. our dear imam has been implicitly described by The Quran many times that shows us His great importance in our religion.  
No one can fully describe the contributions of Imam Ali (AS) to his religion and the people and if anyone dares to do so, he can merely show a drop of the sea. That said we are about to speak about the first question that may occur to our mind: how was our first Imam born?

Birth of the Son of Kaaba, Ali b. Abi Talib

Thirty years after the “year of the elephant” (*) occurrence, in the 13th of Rajab (March 8), when Prophet Mohammad (PBUH&HP) was 30 years old, 10 years before our dear The Prophet (PBUH&HP) received the first revelation from the angel Gabriel and 23 years before the great migration of Muslims from Mecca to Medina.

At this time, our dear imam's pregnant mother (Fatima Daughter of Asad) was praying at Kaaba. She felt an immense amount of delivery pain that she fled to Kaaba from that pain. Suddenly the wall of Kaaba has moved apart and given shelter to her for 3 whole days. After these days, she came out of Kaaba with her dear son, our first imam, Ali b. Abi Talib (AS). Imam’s delivery was a great honor that happened to no one And after yet; walls moving apart, mother’s presence in the holy site of Islam, and the unique birth in Kaaba were all the signs of the greatness of son of Kaaba.
Fatima Daughter of Asad was the second woman that converted to Islam (after Prophet’s wife, Khadija” SA”). She had the honor of taking care of the Prophet (PBUH&HP) from the age of eight until his youth in her (Abu-Talib) house. Their relation was as much close that Prophet (PBUH&HP) called she “mother” So we can see the early strings of Prophet (PBUH&HP) calling Imam Ali (AS) his brother.

Shia point of view about Imam Ali (AS) birth:

1.Sheikh Mofid (died in 413th AH): our first imam, Ali b. Abi Talib (AS) was born on Friday the 13th of Rajab and thirty years after the year of the elephant in Mecca. No one ever has been born in Kaaba before and after him. His delivery was the great honor that God granted him to show his dignity over other men of his age.

2. Allamah Al-Hilli (died in 726th AH): Imam Ali (PBUH) was born on Friday the 13th of Rajab and thirty years after the occurrence of the year of the elephant. No one before and after him, was born in Kaaba at that time, The Prophet (PBUH&HP) was thirty years old.

Sunni point of view about Imam Ali (AS) birth:

Many of the Sunni scholars Believe that Imam’s birth routine was in Kaaba and some of them even think this matter exclusively was only for the Imam.

We will name some of them briefly and look at their point of view:

1. Al-Hakim al-Nishapuri (died in 658th lunar year): a lot of Consecutive narrations have pointed that Fatima bt. Asad have delivered Ali b. Abi Talib in the Kaaba.

2. Sibt ibn al-Jawzi Hanafi (died in 654th lunar year): It has been narrated that when Fatima bt. Asad was pregnant and doing tawaf around the Kaaba, she sensed an immense delivery pain that she fled to Kaaba from the pain; when suddenly Kaaba’s door got opened to her so she went into the Kaaba and gave birth to his child.

Poetry about imam Ali (AS) birth:

Syed Ismail Himayari (who died in 173th AH) was one of the greatest poets of Arabic literature. He wrote a poem about this unique birth:

His mother gave birth to him in God’s safe site; God’s house and masque was his birthplace

He was pure and noble; her mother, her child, and her birthplace too

In one of the darkest nights, he appeared with lunar purity

No child other than Amine’s child is honored like him

References:

1. Kitab al-Kafi (first Volume – page 452)
2. Kitab al-Irshad (first Volume – page 5)
3. I'lam al-Wara bi A'lam al-Huda (first Volume – page 306)
4. Bihar al-Anwar (35th Volume – page 182)
5. Description of Nahj al-Balagha (first Volume – page 6)
6. Manaqib Ale Abi Talib (third Volume – page 307)
7. Rawżat al-Vaeezin (page 81)

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* In that year, Kaaba invaded by faithless king Abraha and his great elephant army and ironically saved by Allah himself with an army of birds carrying small stones by their pecks that penetrate the elephant's body and skull and all of them got killed, and Kaaba was saved.