What IF? And the End of the Silver and Marvel Age of Comics.
Since their beginnings, Comic Books would “break” from their rigid continuity by have dream sequences: Stuff like Lois Lane gets super powers, or Clark Kent loses his. This idea became so popular that in the early 1960s DC would run a series in all of their comics entitled, “Imaginary Tales.” In these tales Superman would get married, have children and even died. Later DC established a Multi-verse where the same character lived but could have different lives.
In fact, the last story of my Superman, the Silver Age Superman, was entitled “Whatever Happened to the Man of Tomorrow?” The editor wrote, “This is an Imaginary Tale, but then again, aren’t they all?
Marvel, under Stan Lee, never did any of that and Stan insisted on ONE Universe. But Stan left the creative team in 1972 and his assistant, and now my friend, Roy Thomas took over. In 1977 he introduced “What If?” This was not part of the Marvel Age of Comics, it was a reflection of it. Here Roy wrote some terrific tales featuring alterations continuity of Marvel continuity. Roy Thomas who did not want any part of “imaginary stories,” a DC concept. So Roy placed the tales in “other” dimensions or on other worlds. So now, instead of having one solidified Universe, we had a Multiverse. So as we see in the Disney Plus stories, dead characters live, and established characters are not so established.
If there was a marker for the end of the Marvel Age, I would place it here. Or just before here.
Marvel had created the omniscient Watcher, a decade and half earlier. His mission was to observe and often, like Spock did on Star Trek explain the stories. Here he is the narrator of What If, on TV as he was in the comics.
Note: The Silver Age began in 1956 and ended in the mid 1970s.