The Demon Etrigan entered Hell, clawing his way out of the womb of his mother, a demoness. Son of the archfiend Belial, Etrigan quickly rose through the ranks of demonhood, and even the elder demons began to fear him. Belial arranged for his son Myrddin, who would become known as Merlin the Magician, to be trained in the arts of sorcery, so that Merlin might one day bind and control Etrigan, his half-brother. Merlin unleashed Etrigan to battle the forces of Morgain Le Fey, intent on usurping King Arthur's Court at Camelot. After Le Fey's defeat and Camelot's fall, Merlin bound Etrigan to the druid Jason, who became Jason Blood.

The Demon Within

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Blood created a series of lives around the world and amassed occult knowledge, hoping either to free himself from Etrigan or at least tame the demon within. During World War 2 the Demon was unleashed, aiding the first Starman during a conflict with the Icicle and Nazi saboteurs. Etrigan also was called upon to help oppose occult forces such as Klarion, The Witch Boy or Blackbriar Thorn. On more than one occasion, his ferocity was welcomed by occult conclaves with other powerful forces such as the Phantom Stranger, the Spectre, and Swamp Thing.

All the while Etrigan had his own agenda: kill Blood, gain his freedom, and rule Hell. During one foray into Hell, Etrigan seemed to have gained his desire. However, moments after acquiring the Crown of Horns and became King of Hell, Etrigan was tricked by Jason Blood and Merlin into returning to Earth. It transpired that Etrigan's evil acts in recent years had been the result of a spell cast by Morgaine Le Fey and an aged incarnation of Merlin. The curse was temporarily broken but, without the stabilizing influence of the benevolent incarnation of Merlin (slain in a pit of Hellfire along with his evil duplicate), the spell that made Etrigan an evil Rhymer soon took control of him again.

Blood lent his experience to a temporary version of the Justice League of America, and reenforced the Watchtower's occult defenses. After Etrigan helped save the League, Blood returned to Earth, once more seeking ways to end his binding just as Etrigan continued seek more power in Hell.

Etrigan's Ryhme

Jason has to say a Ryhme to transform into Etrigan. The Ryhme has changed over the years. Changing from

Yarva Demonicus Etrigan.

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,

Rise the demon Etrigan! ”

to

“ Change! Change, O form of man!

Release the might from fleshy mire!

Boil the blood in heart of fire!

Gone! Gone! -- the form of man --

Rise, the Demon Etrigan!!"

In fact, When Jason turns into Etrigan Everything he says has to Ryhme.