 Though the concept of a shared universe was not new or unique to comic books in 1961, writer/editor Stan Lee, together with several artists including Jack Kirby and Steve Ditko, created a series of titles where events in one book would have repercussions in another title and serialized stories would show characters' growth and change.Headline characters in one title would make cameos or guest appearances in other books.Eventually, many of the leading heroes assembled into a team known as the Avengers.