(except for the obvious) The Best Idea Marvel Ever Had Was...

[DrNewGod]

Spider-Man and The Fantastic Four are off the menu. Beyond that, what was the best idea Marvel ever had?

[Hybrid]

Not sure if this counts because this happened in FF, but it's not the FF themselves. I'll just throw it out there:

Namor appearing in FF as a hobo that Johnny takes in, then gives a shave triggering his memories and welding the Timely era into the continuity.

Think of it as the shared Marvel Universe at Ground Zero.

[DrNewGod]

Not sure if this counts because this happened in FF, but it's not the FF themselves. I'll just throw it out there:

Namor appearing in FF as a hobo that Johnny takes in, then gives a shave triggering his memories and welding the Timely era into the continuity.

Think of it as the shared Marvel Universe at Ground Zero.

That works

[K7P5V]

Definitely the creation of the THUNDERBOLTS

[Revolutionary_Jack]

Archie Goodwin and Roy Thomas taking the license for Star Wars. It saved Marvel at a time of low sales.

[Hybrid]

Stan Lee came up with the concept of mutants out of lazy writing. When he was working on what would become X-Men, he had the five students and their Professor's power sets down, but couldn't think of a way to explain how all of them got their powers. So he just said "they were born with it, mutants" and went from there. Furthermore, the idea of using mutants as an allegory for racism or any discriminated minority stems from that, specifically the idea that mutants themselves are a special minority of people born with their powers and that racism in real life is illogical so a superhero version should be as well.

I think it worked well.

[Surf]

Jim Shooter as EIC. The 80s books flourished under him and getting licences for GI Joe and the Transformers hooked kids like me in the 80s.

[DrNewGod]

I'd say the villain swapping that began as early as the Avengers first tangle with Sub-Mariner. You saw a lot more of that kind of trading later. This went beyond team titles, or having characters guest in each others' titles or features. It gave a subtle richness to the notion that this was a single environment, where the events of one comic had meaning for another.

[Kirby101]

Continuity and a truely shared Universe. That books were part of a long ongoing story. And the emotional life of the characters mattered as much as the adventures.