The Demon is a DC Comics superhero series created by comic book master, Jack Kirby. The title character, named Etrigan, is an actual demon from Hell who usually finds himself allied to the forces of good. Etrigan resembles a squat, muscular human with orange (or yellow) skin, horns, red eyes, and ears resembling bat wings.

He was originally summoned by the wizard Merlin as part of a last-ditch defense of Camelot against the evil wizard, Morgan le Fay. When it became clear that the kingdom would fall regardless, Merlin sent the demon away and changed him into an immortal human named Jason Blood to wait until he was summoned. Later accounts retconned this, so that Blood is now an actual human, bonded involuntarily to the demon as its jailer.

Centuries later, Jason was called to the crypt of Merlin and discovered a poem that could change him into Etrigan. Unfortunately, he was followed by the long-lived Morgan who lusts for Merlin's secrets. That led to Etrigan's first major battle, and to the solidification of Morgan as a major enemy. In addition, he later gained another enemy in Klarion, the Witch Boy, a permanently prepubescent mage who maliciously enjoys creating trouble with his magic.

While his first monthly comic book series was short-lived, and his second was cancelled after five years, Etrigan remains a popular supporting character with occasional additional mini-series. Popular series in which Etrigan has appeared include The Sandman and Swamp Thing.

Some time after his first appearance, Etrigan began speaking entirely in rhyme (the quality of which varied considerably depending on who was writing him at the time). This was explained in-story as the result of a promotion, with the rhyming speech being a badge of his new rank in the infernal hierarchy.

Recently, Jason Blood was recruited by Batman to join a temporary Justice League team.

Jason Blood/Etrigan has made a single guest appearance in each of Batman: The Animated Series (in which he was voiced by Billy Zane) and Justice League (in which he was voiced by Michael T. Weiss). The animated television version of Etrigan does not speak in rhyme except when reciting the spell that changes him between his human and demon identities.

The poem that releases Etrigan is:

Change, change the form of man.

Free the prince forever damned.

Free the might from fleshy mire.

Boil the blood in heart of fire.

Gone, gone the form of man,

and rise the demon Etrigan!

Generally, only the last two lines are actively recited, and the words have been known to vary slightly; the phrase "yarva daemonicus etrigan" has occasionally been used, but not consistently.

The reverse spell is "Gone, gone O Etrigan! Rise again (or once more) the form of man!" The spell itself does not need to be recited by Jason or Etrigan to be effective, merely within their range of hearing and in a pinch, writing it is sometimes sufficient; on one occasion, Blood released Etrigan by using a parody of the spell ("Gone o little man so tame / and rise the demon Whatsisname").