Hellboy was a half-demon brought to Earth by a portal. Raised as a Catholic and with kindness, he became a member of the Bureau for Paranormal Research and Defense (B.P.R.D.), where he often encountered and fought malicious paranormal entities. He was also the last living descendant of Arthur Pendragon on his human mother's side, making him the rightful king of England - a title he denied.
Hellboy appears in The Savage Dragon issue 41, attending Barney Runningbear and Ricochet's wedding, which is also attended by the Ninja Turtles.