Although it does not say it directly in the film, Hancock was once the Greek god Zeus. And this is why?
(1) He is potentially immortal and has lived long enough to be living at the same time as the ancient greeks (at least 3000 years old).
(2) The eagle symbol he wears: The symbol for zeus.
THE AETOS DIOS was a giant, golden eagle which served as Zeus' personal messenger and animal companion. According to some, the eagle was once a mortal king named Periphas, whose virtuous rule was so celebrated that he was came to be honoured like a god. Zeus, in anger, would have smote him with a thunderbolt, but Apollon intervened and, transforming the king into an eagle, set him beside the throne of Zeus. In other accounts, Zeus adopted the eagle as his bird when it first appeared to him before the Titan War as a sign of good omen. The eagle was later sent by Zeus to carry the handsome youth Ganymedes up to heaven to become the cupbearer of the gods.
(3) When Hancock asks Mary what there relationship is, she first tells him that she is his sistor and later that they were married. Hera was the wife and older sister of Zeus, making Mary the greek god Hera.
(4) When Hancock said Mary was crazy, it really got to her...if you read more about Hera, she was a bit of a nutjob.
There may be other connections I missed so let me know. What do you guys think?