Accelerator (方通行アクセラレータ: Ippō Tsūkō (Akuserarēta), lit. "One-Way Road") is the second protagonist in the A Certain Magical Index (Toaru Majutsu no Index) series. He is the 1st-ranked Level 5 and the strongest esper currently residing in Academy City.
Accelerator's ability is Vector Transformation (ベクトル変換 | Bekutoru Henkan). It allows him to control vectors — any objects with a magnitude and direction. Some examples include, but not limited to, are killing viruses, hacking computers, reflecting sound, deflecting bullets, and stopping Earth's rotation. It is passive and active in usage, making him almost invincible. Accelerator normally applies this ability for defensive and offensive purposes, though its applications are limitless. Because of his massive intellect and calculating prowess, he can quickly understand and apply unknown/strange laws (e.g. dark matter) through the world of numbers.
He normally reads manga and drinks coffee in his free time and is somewhat lazy. But when he is enraged or excited such as when fighting a strong or amusing opponent, he breaks into a wide grin and laughs, giving him a maniacal and sadistic appearance.
"I strive for something beyond the strongest, that challenging me would be the most ridiculous thought ever, that fighting me would be a sin!" ~To Misaka 10032 in Vol. 3~