The unknown killer
Accelerator appears as a skinny teenager and has pale skin, moppy white hair and red eyes. This is caused by his ability, as it blocks ultraviolet rays, thereby preventing his body from producing melanin. His ability also reduces the outside influence so much that it causes a loss of balance in his hormones, giving him what he calls an "androgynous appearance," although there is definite evidence stated throughout the series that he is a boy. While in the novel he is shown to have a slim, androgynous body, a bathing scene depicted him as bare-chested and obviously male.
Much of his past is unknown, but Accelerator mentions that he once had a "normal name" which has yet to be revealed, and most likely never will, as Accelerator himself forgot it. The novels state that his last name consists of two kanji and his first name three, yet his name had no real meaning to it.