Stryfe is the clone of Nathan Christopher Summers, alias Cable, the son of Cyclops of the X-Men. Nearly two millennia in an alternate future, the aged mutant Mother Askani, alias Rachel Summers, led the Askani cult which opposed the rule of Earth by the long-lived mutant tyrant Apocalypse. In need of a powerful warrior who would oppose Apocalypse, Mother Askani sent a female member of the cult back to the X-Men's own time period. The Apocalypse of that time infected the infant Nathan Christopher Summers with a techno-organic virus that was rapidly spreading through his body and, if not stopped, would kill him. The Askani cult member persuaded Cyclops to let her take the infant to the far future, where advanced medical science could save his life.
Once the infant Nathan had arrived in the Askani's time, Mother Askani had him cloned, so that if Nathan himself died, the cult could raise his clone to be their savior. The clone's growth was greatly accelerated until he was the same age as Nathan himself. The Askani succeeded in halting the spread of the techno-organic virus in Nathan's body, thereby saving his life.
However, Apocalypse and his forces then invaded the Askani's hiding place. Apocalypse found the infant clone and decided to raise him himself.
The Askani took the original Nathan to safety, and he was raised to early adolescence by Cyclops and his wife Phoenix, whom Mother Askani transported to the Askani's time period.
Apocalypse named the clone Stryfe and encouraged the boy's arrogance and cruelty as he grew into adolescence. Stryfe was watched over by Apocalypse's aide Ch'vayre, who regarded the boy's malevolence with mixed feelings. Neither Apocalypse nor Stryfe was aware that Stryfe was actually a clone.
At this point in Apocalypse's millennia-long existence, he had to transfer his consciousness and life forces from one body to another to maintain his life. When his current body grew too old and feeble, Apocalypse intended to take over the powerful young body of Stryfe.
Apocalypse's plans were thwarted, however, when he was killed by the adolescent Nathan Summers, who became known as Nathan Dayspring Askani'son, and later as Cable. Stryfe went into hiding with Ch'vayre and eventually became the military leader of the new dictatorship that arose in Apocalypse's place, the New Canaanites.
Cable, meanwhile, became the foremost military leader of the New Canaanites' opposition, the Clan Chosen. During the war between these opposing forces, Cable and Stryfe clashed repeatedly, becoming bitter enemies, even though neither was aware of the true relationship between them.
Eventually Cable went back in time to the Twentieth Century, hoping to change the course of history by stopping Apocalypse back then. Stryfe fled to the Twentieth Century himself and organized the terrorist group called the Mutant Liberation Front.
Inevitably, Cable and Stryfe came into conflict yet again, first when Cable headed the mercenary team called the Six Pack, and later after Cable had taken over the New Mutants, whom he reorganized into X-Force.
At one point Stryfe ordered the massacre of the Native Americans of the Camp Verde Reservation, the original home of X-Force member Warpath, in order to cover up secret, illegal genetic experimentation being conducted in its vicinity.
Posing as Cable himself, Stryfe publicly made an assassination attempt on Professor Charles Xavier, founder of the X-Men, and nearly succeeded in killing him. Stryfe defeated Apocalypse and seized control of his team of superhuman warriors, the Dark Riders. Believing himself to be the real Nathan Summers, Stryfe captured Cyclops and Phoenix, blaming them for abandoning him as an infant.
As a means of spreading further destruction, Stryfe also introduced the Legacy Virus, a disease genetically engineered to be lethal to mutants, into present day Earth. The Legacy Virus has since infected a large number of mutants and killed many of them.
Ultimately, Cable and Stryfe had their climactic battle on Earth's moon. They fell through a time vortex and were seemingly destroyed by a self-destruct device in Cable's battlesuit. In fact, however, Cable survived while Stryfe's body was annihilated.
But Stryfe's consciousness projected itself into Cable's own mind and took control after Cable returned to Earth. Eventually, however, Cable's mind reasserted control, and Stryfe's consciousness left his body.
Later, Warpath was injected with drugs by the criminal scientist Edwin Martynec that stopped his heart. Warpath's spirit was transported by Stryfe's spirit to the netherworld ruled by the demon Blackheart. Blackheart had promised to let Stryfe return to the world of the living in Warpath's body if Stryfe could defeat Warpath's spirit. But instead Warpath's spirit defeated Stryfe and returned to his body, thereby coming back to life. Stryfe, on the other hand, remains a prisoner in Blackheart's netherworld.