In 1961, writer-editor Stan Lee revolutionized superhero comics by introducing superheroes designed to appeal to more all-ages readers than the predominantly child audiences of the medium. Modern Marvel's first superhero team, the titular stars of The Fantastic Four #1 (Nov. 1961), broke convention with other comic book archetypes of the time by squabbling, holding grudges both deep and petty, and eschewing anonymity or secret identities in favor of celebrity status. Subsequently, Marvel comics developed a reputation for focusing on characterization and adult issues to a greater extent than most superhero comics before them, a quality which the new generation of older readers appreciated. This applied to The Amazing Spider-Man title in particular, which turned out to be Marvel's most successful book. Its young hero suffered from self-doubt and mundane problems like any other teenager, something readers could identify with.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What was Marvel's least successful book?
unanswerable