Asura Ōtsutsuki

He was the younger son and heir of the Sage of the Six Paths.

Background
He inherited the Sage's "body", 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 Uchiha clan, would continue this fight with the younger brother's descendants, who would become the Senju clan.

Appearance
He has short spiky hair with two locks of hair wrapped in bandages framed either side of his face in a similar manner to his brother. He also wore what seemed to be a forehead protector with markings on the sides but no symbol on the metal piece.

Trivia

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