Jason Blood is an expert in the occult and demonology from the 6th century. When the demon Etrigan was ravaging the area, Merlin bound the demon to Jason. From then on, Jason of the Blood has become an immortal being who can transform from man to demon upon uttering the rhyme:
Change! Change! O’ form of man!
Free the prince forever damned!Free the might from fleshy mire!
Boil the blood in the heart for fire!
Gone! Gone! O’ form of man!
Rise the demon Etrigan!
His human side curbs the evil malevolence of Etrigan and the end result is a bit of a bawdy antihero. Jason Blood is immortal to the effects of age, able to use a wide variety of magic, and has all the martial knowledge of 15 centuries...which is a lot! This particular iteration of Jason Blood is from the Demon Knights comics. This is set in the Medieval era of DCU's universe, where Etrigan is working with Madame Xanadu through an exciting storyline that involves Hell, undead knights of Arthur's court, Vandal Savage and the murder of Merlin. Cool stuff!
This figure was bought just out of a pure desire for a really cool-looking demon figure. I have no particular attachment to Etrigan, though I do love his rare appearances in DC animated movies (which is the only decent way DC can do shows or films, fight me!).