Accelerator

History
The Accelerator (一方通行 (アクセラレータ) Ippō Tsūkō (Akuserarēta)?, lit. "One-Way Road") is the name used to refer to the 1st-ranked Level 5, the strongest esper currently residing in Academy City.

He is the second protagonist of the Science Side in the Toaru Majutsu no Index series. First appearing chronologically in Toaru Majutsu no Index as an antagonist, he later becomes the primary male protagonist of the Science Side after being defeated by Kamijou Touma. His journey to a more "heroic" role in the story progresses after meeting and saving Last Order, and is forced into an ironic twist of fate where his life now depends on the Sisters, clones he previously killed by the thousands. He is also a major antagonistic character in Toaru Kagaku no Railgun and the protagonist of Toaru Kagaku no Accelerator.

In his role as a protagonist, he is forced to deal with the cruel Dark Side of Academy City and the secret conspiracies surrounding it. As the most powerful esper of Academy City, his existence and powers are tied to the plans of Aleister Crowley, the founder of Academy City, alongside Kamijou Touma.

More Information: http://toarumajutsunoindex.wikia.com/wiki/Accelerator