If Terah was 70 years old when Abraham was born,1 and if Sarah was born 10 years later,2 Terah was 80 when he fathered Sarah, which was certainly near the biological limits. At the very least, he was an old man, and it's no surprise that he died immediately after moving to Harran. It also wouldn't be a surprise if somebody in Shuttarna's court took in the children and raised them after Terah's passing, Abraham being 10 years old, and Sarah being just a baby. Who was the foster parent? One candidate is certainly worth considering.
Abraham's older step-brother was Tushratta, who got his name from the Sanskrit Tvesa-ratha, which means "his chariot charges."3 So he was a Mitannian, with an Indo-Aryan heritage. He might also show up in Hindu legend as Dasharatha,4:55 who was known for his magical chariot. Since "D" and "T" were interchangeable at the time, we should consider Dasharatha & Tushratta to be alternate spellings of the same name, with the reference to chariots serving as confirmation. This doesn't tell us whether it was the same person, or two different people with the same name, which of course happens all the time, especially over such distances. So we need more clues if we are to make an identification with any degree of confidence.
Dasharatha grieving at his obligation to banish Rama.
In the Hindu Ramayana, King Dasharatha favored Rama, and it broke his heart when he had to send Rama away, such that a son by another marriage would become the crown prince. If Dasharatha was Tushratta, Rama would have been Abraham. If so, the reason for the banishment would be simple — Abraham would have been adopted, and not even a native Mitannian, giving the biological sons stronger claims to the throne. Once exiled, Rama's wife Sita was kidnapped by a foreign king, and Rama had to spend 14 years fighting to get her back. This matches Sarah being married to Amenhotep III for 15 years ().4:52 In one version of the Ramayana, Sita's mother was the foreign king's wife, while Sarah's sister Mutemwiya was Amenhotep III's mother, so both stories have the king & "kidnapped" princess as close relatives. There are enough parallels (here and a few more below) to make a good working hypothesis out of Tushratta being the inspiration for the legend of Dasharatha. And reading in the details from Dasharatha's story makes Tushratta a good candidate for Abraham's foster father. It's even possible that "Terah" was just a shortened form of Tushratta, with the name of Abraham's biological father being lost to history. If so, when Joshua said that Terah worshiped other gods,5 he would have been referring to Tushratta worshiping Mitra, Varuna, Indra, and Nasatya.6
More interesting still is the possibility that Abraham was the (adopted) son of Tushratta who succeeded him as king of Mitanni,4:55 after one of his biological sons killed him. There isn't much to go on here, but it's easier to believe that Abraham, not a native Mitannian, brokered the alliance with the Hittites that restored order after Tushratta's death. If so, Abraham showed up in the secular records as Mattiwaza. (As such, his name might have been preserved in Hebrew as Mathiew.4:55) Some historians consider Mattiwaza to have been a brother of Tushratta, while others take him to have been a son. In the present thesis, Abraham was the step-brother and adopted son of Tushratta, hence the ambiguity. Mattiwaza went to Hatti when the political situation in Mitanni became unstable, whereupon he married Suppiluliuma's daughter, and returned to Mitanni with a Hittite army to settle the issue of succession. The year would have been , just after the First Syrian War, in which Suppiluliuma took advantage of the turmoil in Egypt and Mitanni to expand his territory.7:107 Sarah had passed away in (as estimated in the article on The Historicity of the Patriarchs), and Isaac had married Rebekah (i.e., Tadukhipa, who disappeared from the Egyptian records after ). Then Abraham married Keturah.8 This could have been the daughter of Suppiluliuma. In just this period, the Hittites in Hebron addressed Abraham as a mighty prince,9 which would have been appropriate for the son-in-law of Suppiluliuma. Akhenaten would have given his blessing, being too busy building Amarna to worry about it, and if it meant that somebody with ties to Egypt would gain control of Mitanni. The pharaoh even implicitly ceded some of Syria to Suppiluliuma as part of the deal, by pulling out his ally Aziru, and then holding back his military commander (i.e., the future pharaoh Horemheb), and withholding support from his other vassals, making the conquest easy. Both Muhammad and Al-Tabari said that Abraham came after Aziru,10,11:120 which is difficult for other chronologies, but which falls right in line if Abraham was Mattiwaza — Aziru's territory was left to Suppiluliuma in the First Syrian War, and shortly thereafter, Abraham-Mattiwaza was installed as king of Mitanni.
In the Ramayana, Rama returned home to become ruler, though there was a falling out with Sita amidst accusations that she had gone voluntarily with the foreign king. With Abraham returning to Mitanni to succeed Tushratta, the issue with Sarah might have been different, but it might have sounded the same — as the former wife of Amenhotep III, she might have been prevented from following Abraham back to Mitanni if he was to rule there, since no Egyptian queen had ever gone with a foreign ruler.12:64 Isaac was also prevented from going back to Mitanni — a Mitannian bride was provided for him, under the supervision of the pharaoh's agent,13 but he himself never left Canaan. The Torah doesn't say why, but if Isaac was the son of Amenhotep III, he was the half-brother of Akhenaten, and his presence in Harran would have alarmed the Mitannians, not to mention infuriating Suppiluliuma. He also wouldn't have been able to take Rebekah with him, since she was a former wife of Amenhotep III & Akhenaten, and therefore couldn't have taken up residence in a foreign court. With Abraham's wife & son staying behind, the authors of the Ramayana noted the divided loyalty, albeit under the assumption that Sarah's opinion was a factor, which wasn't necessarily the case. She might have actually felt both enslaved by the pharaoh, who wouldn't let her follow Abraham back to Mitanni, and abandoned by Abraham, who then chose the throne of Mitanni over her. But of course the story told in Harran would have been Abraham's version — perhaps from his point of view, Sarah had betrayed him, placing a higher value on her titles in Canaan than on her husband, and that's the version preserved in the Ramayana.
After getting banished from Rama's realm, Sita produced twin sons. If this was Sarah, she would have been too old by then, and the reference would have been to her twin grandsons Esau & Jacob, born .
Abraham didn't live much longer, being 70 years old in . While still alive, he sent the sons he had by Keturah "to the east country" to avoid a conflict with Isaac,8 just as he had been forced earlier to send away Hagar & Ishmael,14,15 such that the Covenant would pass exclusively to Isaac. The "east country" wouldn't have been Mitanni or Babylon, or the scribes would have said so, as they did in so many other places. So the "east country" would more likely have been India. If Abraham's sons were sent there in , it becomes possible for his story to get written deeply into Hindu lore, which was being formulated at the time.
Why would such significant information be omitted from the Torah? The answer might be just that it wasn't all that significant to Sarah or Isaac, whose descendants inherited the chronicle. And Mitanni would never be significant again, thereafter being either Hittite or Assyrian territory. So Abraham's brief stint as king of Mitanni was an unimportant tangent not worthy of mention in the Torah. Much more important things were about to happen in Canaan, which would have a far more profound effect on the emerging Jewish culture. So they left it up to their cousins in Punjab to preserve that chapter of Abraham's story.
Thus the timing was right, and the political situation was plausible, for Abraham to have been Rama, whose Mitannian name was Mattiwaza, step-brother and adopted son of Tushratta. The Torah and the Ramayana fit together with each other, and with the secular history, on lots of points. And it's easier to believe that the Hindus got their legend of Dasharatha & Rama from real people in Mitanni, than to think that they adopted some of their legends from Sumerians and/or Minoans and/or Mycenaeans, as some scholars have argued. The link between Punjab & Mitanni was strong, due to their common Bactrian heritage, while links to other cultures were weaker. In time, the Indians would forget that the name Rama came from Abraham, which itself came from Brahmin, meaning that he was raised as a Hindu priest, albeit in Harran instead of Ayodhya.
Why didn't the Indians preserve the actual details of Abraham's adventures, such that the identification of him with Rama would be more explicit? Some scholars believe that until the , Ayodhya was just a mythical city.16 Then Skandagupta (who reigned ) moved the capital to Saketa, and renamed it Ayodhya, establishing a more material seat for the Ramayana. But Ayodhya might have been a real place elsewhere. If the present thesis is correct, Abraham's ancestral homeland was Bactria (putting Ayodhya on the Amu Darya river). If so, this would have been awkward for Skandagupta, who had just repelled an invasion of Bactrians. So the people had religious & cultural ties to a region that had become the political adversary of Skandagupta, who solved the problem by rewriting the history of Ayodhya.