Exiled

With the ability to mimic the powers of mutants, Calvin Rankin served as both an ally and an enemy to the original X-Men.

Although he never joined the Defenders in the mainstream Marvel Universe, the version of Mimic who joined the dimension-hopping Exiles told how he had been a member of the Defenders in the a parallel universe he called home (Exiles #3).

Mimic: Yes, not my finest hour. You should have seen my costume…

It's unclear if the costume Mimic wore with the Defenders was the same costume worn during his original X-Men appearances.

When the Exiles journeyed to an alternate timeline where the X-Men prepared to fight the Imperial Guard to save Jean Grey/Dark Phoenix (mirroring X-Men #137), that world's version of Wolverine was surprised to see Mimic.

Wolverine: So what's up, bub? Ain't you supposed to be running around with Doc Strange and Iceman?

That line of dialogue revealed that the Iceman of this alternate reality was already a member of the Defenders during the historic Dark Phoenix saga, whereas the Iceman of the mainstream Marvel Universe was away at college at that point—and joined the Defenders only later, as the non-team transitioned into the New Defenders.

We can only imagine what other ways the Defenders of this world might have been different.

Exiles. Vol. 1. No. 3. October 2001. "Old Wounds, New Battles: Part 1 of 2." Judd Winick (writer), Mike McKone (pencils), McKenna w/Cannon (inks), Transparency Digital (colors), Sharpefont's Paul Tutrone (letters), Mike Raicht (assistant editor), Mike Marts (the editor), Joe Quesada (the watcher), Bill Jemas (the beyonder).