Fantastic Four #176, published in August 1976, took the series into Marvel Comics' own offices for an unusually self-referential encounter involving the Fantastic Four, the Impossible Man and Stan Lee. The issue was written by Roy Thomas, drawn by George Pérez, and inked by Joe Sinnott, with a cover by Jack Kirby.
The story followed the events of the previous issue, in which the Fantastic Four tried to stop Galactus from devouring Counter-Earth. The Impossible Man offered his own world instead, but Galactus suffered what appeared to be cosmic indigestion after consuming it. The Fantastic Four and Impossible Man then returned to Earth, while Ben Grimm was once again trapped in his mutated Thing form.
After arriving on Earth, the Impossible Man discovered that Marvel Comics existed within the Marvel Universe. The issue presented the publisher as the official chronicler of the Fantastic Four's adventures, recording events based on information supplied by the team.
The Impossible Man wanted Marvel Comics to produce a comic about him. When the staff refused, he began wrecking the company's offices, forcing the Fantastic Four to confront him inside the workplace. Pérez's artwork included likenesses of several Marvel creators, including Roy Thomas, Stan Lee, Jack Kirby, Marie Severin, John Verpoorten, Archie Goodwin, Marv Wolfman and Gerry Conway.
To end the conflict, Reed Richards captured Stan Lee and used him to make the necessary deal. Lee reluctantly agreed to give the Impossible Man his own comic, although he later went back on that promise. The result was a story that turned Marvel's editorial offices and recognizable creators into part of the Fantastic Four's fictional world.
Sources: Comic Book Resources.