Archer

Archer is actually a future version of Emiya Shirou, who became a hero through Emiya's wish to save innocent lives. After his death he became a Counter Guardian, a Spirit deployed to maintain balance and prevent humanity's extinction, but without the ability to act on his own he was forced to kill and face the fact that his ideals were not realizable time and time again. To escape this cycle the only hope for EMIYA was to be summoned as a Heroic Spirit and kill his past self before he became a Counter Guardian, which would cause a time paradox and release him from the cycle.!~