[1] Bastion is introduced as Sebastion Gilberti, a mysterious man who had risen to power in a relatively short time in the U.S. Government and began assembling the international anti-mutant strike force Operation: Zero Tolerance (OZT).

Jean could not read Bastion's mind, but he easily identified the two X-Men hidden among representatives of various foreign intelligence agencies interested in supporting OZT.

[8] After learning of the Prime Sentinels' nature, the President was convinced by Senator Robert Kelly and Henry Peter Gyrich to suspend Bastion's operations.

[9] While in government custody, more mysteries surrounding Bastion were discovered, but before a further investigation could be made, he managed to escape and return to the home of his mother figure Rose Gilberti.

The merging of the two Sentinels into a single being with no memory of his past, Bastion was eventually found by Rose who took him in and taught him human kindness.

Bastion was, however, able to co-opt and integrate itself with one of the Gatekeeper's bodies and used it to attack the techno-organic hero Warlock and his allies, being eventually defeated.

Bastion rewrote its programming and infected Donald Pierce and the Leper Queen, the recovered techno-organic remains of Cameron Hodge and Steven Lang, as well as the corpses of Bolivar Trask, Creed, and Reverend William Stryker with the Technarch transmode virus, declaring them to be the future of humanity and the end of mutantkind.

[19] His first move was to capture several mutants and inject them with a strain of the Legacy Virus to cause their powers to go berserk and kill themselves and thousands of humans.

While claiming that Bastion's current programming makes him difficult to sway, Quasimodo states that would be a beneficiary tool if they can find a way to bypass his Prime Director.

When rebooting, Bastion takes on much of Nimrod's old appearance, but is finally destroyed when Hope manifests a variety of the current X-Men's mutant powers and obliterates him.

He eventually returned to the present and was soon confronted by the time-displaced X-Men which confirm that Bastion's actual goal is simply to preserve mutants until their population rises to a level where he can destroy them all himself.

[26] Bastion went with Havok to take control of an army of Prime Sentinels; since his programming was unrecognizable by them, they identified him as a threat despite his role in their creation.

[27] After Sebastian Shaw failed in his attempt to kill Magneto to gain a role in the Mothervine plot, Bastion was present to negotiate with and later fight the Master of Magnetism, simultaneously unleashing a wave of Prime Sentinels to finally release Mothervine under Havok's order; Magneto was able to escape by using a vial of Mutant Growth Hormone and throwing a lighthouse at the group, fleeing in the chaos.

[30] The traitorous Frost, disillusioned by the Mothervine plot, freed Polaris and her team after overseeing an experiment by Miss Sinister on Jimmy Hudson, and they made their way to the inner circle's meeting room.

At this point, Magneto had discovered the mutant Elixir who was capable of reversing the Mothervine mutations and was taken across the world to stop the rampancy, to the notice of Havok and Bastion.