Mana Walker is the adopted father of Allen Walker.
Not much is known about Mana's past history aside from his profession as a clown.
Mana Walker is a character created by Hoshino Katsura for the series D. Gray Man.
Mana had a brief role in the story. However his personality took a drastic change when his brother Nea Walker died.
Mana was a middle aged man of average height and build. He had short trimmed black hair.
Mana was a humorous person. As a clown by profession, he would tend to act comical and cheerful. When his brother Nea died however, his personality changed drastically to that of a distant and passively angry man.
Allen Walker - His adopted son.
Mana found and adopted Allen Walker when he found him abandoned by his parents because of his deformed left arm. He treated Allen like his son and they made their living as professional clowns. However when Mana Walker's brother Nea Walker passed away, Mana became a changed man. He was not kind to Allen anymore and his health declined, causing a rapid progression towards his eventual death.
Allen was overcome with grief, but he was approached by the Earl of Millennium. The Earl assured Allen he could bring Mana back to life if he agreed. Allen did so, but he was tricked. The Earl brought Mana back to "life" as an Akuma. Mana was furious with Allen for being so naive and slashed Allen's face, which caused Allen's pentacle eye to develop. Out of pure reaction, Allen's deformed arm awakened and took it's true innocence weapon form, and Allen instantly destroyed Mana Walker's new Akuma form. Before Mana died though he told Allen that despite what had transpired, he loved him. Then Mana perished, leaving such a traumatized Allen that the young boy's hair turned white.
Mana Walker had no powers as a human but he was a professional clown.
As an Akuma it can be assumed that he had the standard abilities of a level 1 Akuma.