Marvel Comics has built up what might be the most creative, well-known, and iconic universe of characters that pop culture has ever known. Set in the 616 universe, the main stories at Marvel follow a variety of superheroes and their teams in their adventures and battles against the forces of evil. Characters like Spider-Man debuted in sought-after, famous comics that people recognize by name alone. However, even Marvel's first Captain Marvel debuted in an obscure title.
Source：https://www.cbr.com/superheroes-villains-obscure-cameo-first-appearance-marvel-comics/
