Asura Ōtsutsuki

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

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

Personality
He believed that love was the ultimate key to peace, and loved his father greatly as well.

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.

Abilities
While virtually nothing is known of his abilities, he inherited his father's incredible life force and physical energy, and also fought using a shakujō which he was presumably skilled at wielding.

Trivia

 * As the younger brother was born with the "willpower" of the Sage of the Six Paths and desired peace, it may be possible that Hashirama Senju's "Will of Fire" refers to this. Similarly his brother's descendants rose to oppose this, inheriting the "Curse of Hatred".
 * Like his father, he wielded a shakujō in battle. His choice of weapon could represent his desire for love and peace while his brother's choice of a sword could symbolise his lust for power.