From a Golden Age: The Invaders Appreciation 2019

[Reviresco]

The Invaders were created by Roy Thomas, out of his love for the Golden Age era characters. They first appeared in Avengers 71, cover date December 1969, though they weren't called Invaders, and they only consisted of Namor the Sub-Mariner, The Original Human Torch and Captain America. But Roy did have Jim Hammond yell their battle cry "Okay Axis, Here We Come!" in this issue when they fought Yellow Jacket, Black Panther, and Vision as champions in a cosmic contest between Kang and the Grandmaster.

The Invaders sort of appeared again in Avengers 97, cover date March 1972, as heroes "summoned" by Rick Jones during the Kree-Skrull War.

They finally appeared as a team named Invaders in an origin story that appeared in Giant Sized Invaders 1, cover date June 1975, with art by Frank Robbins, inked by Vinnie Colleta. And while Churchill gives them their name in the story, according to Roy Thomas' Recollection page in Giant Sized Avengers 1:

And thus was started the Invaders first ongoing, which ran for 41 issues, an Annual and this Giant Sized issue.

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First posts were written by Rheged and are from the previous appreciation thread, which can be found here:

From a Golden Age: The Invaders Appreciation 2014-2018