The Endless are a family of seven anthropomorphic personifications of universal concepts, around whom much of the series revolves. From eldest to youngest, they are:
Cain and Abel are based on the Biblical Cain and Abel and adapted by editor Joe Orlando with Bob Haney (writer) and Jack Sparling (artist) (Cain), and Mark Hannerfeld (writer) and Bill Draut (artist) (Abel). They were depicted together in Abel's first appearance, and parted to their respective Houses at the end of the story. Although Cain would abuse Abel, he was not shown killing him until Swamp Thing vol. 2 #33. In Elvira's House of Mystery #11, Cain expresses shock at having killed his brother in recent times. In the same issue, a contest-winning letter establishes that Cain and the House exist both in the dream world and the real world, and that only in the dream world Cain continues to harm Abel. In The Sandman, Cain is shown to kill Abel quite often. In issue #2, Lucien calls this unusual, and recent.
Originally they were the respective "hosts" of the EC-style horror comic anthologies House of Mystery and House of Secrets, which ran from the 1950s through 1983—Cain debuting in House of Mystery #175 (1968) and Abel in DC Special #4 and House of Secrets #81 (both 1969). During the 1970s, they also co-hosted the horror/humor anthology Plop!. They were also both recurring characters in DC's Elvira's House of Mystery (1986–88).