Etrigan

Etrigan is a fairly low order demon, but he's tied to one Jason Blood by way of a curse, although things keep happening to screw that up.

Twitterpated djfanboy 2008

In the Justice League cartoons that had magic villains they had to have guest stars like Etrigan the Demon and Dr. Fate help out, which is probably why it worked, with the magical heroes doing the magic stuff and the Justice League doing regular fighting.

Superhero Nation: how to write superhero novels and comic books » Stefan’s Review Forum 2009

The book puts the classic Jack Kirby creation "Etrigan the Demon" -- an ill-tempered fiend with a penchant for rhyming bound by the wizard Merlin to the mortal Jason Blood, a knight of King Arthur's Round Table -- at the center of a motley group of characters in the medieval age.

Turnstyle: DC's Epic Dark Fantasy: Paul Cornell Talks 'Demon Knights' Turnstyle 2011

Not all these guys are noble, Etrigan especially doesn't want to be that, but you know, some of them are fighting for themselves.

Turnstyle: DC's Epic Dark Fantasy: Paul Cornell Talks 'Demon Knights' Turnstyle 2011

Solomon Grundy #1 - Cyrus Gold apparently struck a deal with Satan and now has to deal with Spectre, Phantom Stranger, Sentry, Etrigan, and (coming soon) Bizarro.

Quick Hits – Kolchak Tales, The Mighty, Dead of Night: Werewolf by Night, and More 2009

It looks like Aquaman and Etrigan are trying to remember where they parked their car.

What’s Aquaman up to? | Major Spoilers - Comic Book Reviews and News 2009

Solomon Grundy #1 - Cyrus Gold apparently struck a deal with Satan and now has to deal with Spectre, Phantom Stranger, Sentry, Etrigan, and (coming soon) Bizarro.

10 « March « 2009 « Axiom's Edge Science Fiction and Fantasy 2009

Ivy takes over Arkham, luring Bats in (also drugging him with THC) to fight off the weird cannibal demon Etrigan.

[REVIEW] Batman: The Widening Gyre #1-3 « Giant Killer Squid - Film, Comics, News, Reviews and more 2010

A horrifying lost city has risen at the bottom of the ocean, and Aquaman must call on the supernatural might of Etrigan, the Demon to stand between humanity and the dark menace that lurks inside that forgotten realm!

DC Comics for February 2010 | Major Spoilers - Comic Book Reviews and News 2009

Dick and Tim are confronted with their oh-so-obvious family issues and Deadman goes on to jump into Jason Blood to bring out Etrigan.

Comically Challenged: Blackest Night Mini-Series « Giant Killer Squid - Film, Comics, News, Reviews and more 2009