Indra was the first born of Hagoromo's sons. He was gifted with Hagoromo's eyes and spiritual energy, and from birth was a prodigy. He was exceptional and he was all too aware of his superiority, doing everything on his own and feeling that anything could be achieved with might. This didn't bode well for Hagoromo, whom when deciding on which of his sons would succeed him before he died, chose his younger son instead. Indra believed it was his birthright and, upon Black Zetsu's manipulation and goading, fought Ashura for the honor, resulting in their mutual deaths.
He was reincarnated numerous times over the millenium, his most recent reincarnations being Madara and then Sasuke.