In 1993, Mike Mignola introduced Hellboy in John Byrne's Next Men #21, a hero who captivated a generation of comic book fan as the perfect indie occult superhero. Following his breakout solo miniseries, Seed of Destruction, Mignola established an entire shared universe around his Hero with a Red Right Hand. This universe, dubbed the MignolaVerse, contains many great heroes who frequently have their stories told without the inclusion of Hellboy.
Source:https://www.cbr.com/mignolaverse-non-hellboy-comics-ranked/