Sephiroth is the elite fighter of SOLDIER and a revered war hero, as well as the arch-nemesis of protagonist Cloud Strife. Sephiroth went missing after the Nibelheim mission, where he went insane and burned the small town to the ground after finding out that he was created for an experiment; an effort to create a superbeing with the cells of an alien known as Jenova, whom he considered his mother. His biological parents are Professor Hojo and Lucrecia Cresent, Sephiroth was injected with the Jenova cells during the foetal stage. He is best known for killing the last remaining Ancient (people born of the planet, who nurture and communicate with the Planet, and finally return to it), and almost destroying the planet.

Originally the poster boy for strategic genius, bravery and all that good stuff, Sephiroth's fall into madness makes him into a sadistic killer who delights in the suffering of others. His favorite person to torment is Cloud, whom he calls his "puppet." His will is said to be second to none and for this reason, Sephiroth refuses to merge with the Lifestream even after his defeat.

He returns in Advent Children once again, refusing to remain "just a memory."

Also he is left-handed. His long katana is called 'Masamune'.