Asura Ōtsutsuki

The Senju clan ancestor was the younger son and heir of the Sage of the Six Paths.

Background
He was born with the Sage's "body" (the willpower and physical energy) and believed that love was the key to peace. When the Sage was on his deathbed, he selected the younger brother to carry on his dreams of peace for the ninja world. The older brother, believing he should have been chosen, fought him to try and claim what he felt he deserved. His descendants, who would become the Senju clan, would continue this fight with the older brother's descendants, who would become the Uchiha clan.

Appearance
He has short spiky hair and wears what seems to be a forehead protector with no symbol on it.

Trivia

 * As the younger brother was born with the "willpower" of the Sage of the Six Paths, it may be possible that this refers to Hashirama Senju's "Will of Fire".