ALTERNATE VERSIONS
In one timeline, Stryfe’s future was destroyed when the Apocalypse Twins used a tachyon to wipe out all future Earths when the present-day planet was annihilated by the Celestials. This slightly divergent Stryfe was seen occupying a space habitat in 3806 with the present day MLF. He was recruited by Kang the Conqueror for the Chronos Corps before his reality was completely undone and helped orchestrate a plan to undo Earth’s destruction. However, enacting that plan required conflict with the Master of Magnetism on Planet X. Magneto quickly demonstrated how ill-suited the Chaos-Bringer was to fight him by crushing Stryfe to death inside his armor.
In What If..? (2nd series) #69, the climax of the X-Cutioner’s Song played out differently. Apocalypse’s attempt to save Xavier failed, and the repercussions of the professor’s death were felt as far away as the moon. Xavier’s psychic death scream distracted Stryfe and Jean Grey during their walk on the moon, causing Scott and Jean to suffocate and die before Stryfe regained his composure. The truce between the X-Men and Apocalypse fell apart with Xavier’s death, and he killed many of them before advancing on the moon alone. The delayed rescue team meant Stryfe had time to kill Wolverine and Bishop before taking Cable prisoner. Stryfe genuinely lamented his parents dying too soon, and he confessed the full scope of their history to the manacled Cable. Dayspring tried to reach out to Stryfe as a brother, telling him Apocalypse was their one true enemy all along. When a three-way war broke out between Stryfe, Apocalypse and the finally arriving remnants of the X-Men, the heroes were beaten and Apocalypse offered Stryfe the chance to seal their alliance by murdering Cable. Stryfe finally saw the folly of chasing Apocalypse’s approval, and accidentally killing his parents left him hollow and in no mood to kill his brother. Instead, he sacrificed himself to force Apocalypse into his time vortex machine, consuming them both in one final act of heroism after a lifetime of bitterness.
In the Ultimate universe, Stryfe was a very different character. From the present and with no ties 
to the Summers clan, he was a mutant empath able to provoke negative emotion to stimulate unrest and… strife. He presented as an activist leading the Mutant Liberation Front to oppose the government and the relaunch of the Sentinel program in the wake of Charles Xavier’s death. In truth, he was a self-serving coward who was paid off by Fenris International to agitate mutant terrorism in order for Fenris to justify selling their Sentinels to the government.
In the Age of X-Man, Nate Grey crafted a fabricated history where the human race permanently evolved into mutants following an event called the Resolution. This was the climax of a battle with Stryfe, the final foe the X-Men faced before peace came to their world. Stryfe was reportedly responsible for the deaths of Quicksilver, Scarlet Witch, and possibly many more of the named dead such as Cyclops, Wolverine, Xavier, and more, before Hope Summers used the power of the Lifeseed to end the conflict and enact the Resolution.
In several realities, other characters have taken up Stryfe’s armor for their own purposes. Ultimate Cable was actually a future version of Wolverine, but he once wore armor evocative of Stryfe while fighting Apocalypse. In X-Force (2nd series) #3-6, a future version of Domino took on Stryfe’s mantle and identity and built her own MLF to oppose the Skornn. In Cable and X-Force, Hope Summers adopted Stryfe’s look in a future where she and Blaquesmith constantly manipulated the past to streamline upcoming events.