Nergal was once an antagonist from the show, The Grim Adventures of Billy and Mandy, on Cartoon Network. He is a demon-like creature that lives in the Center of the Earth with his wife, Sis, and his son, Nergal Jr. He has eight snake like tentacles that shoot out electricity.
Nergal was first voiced by David Warner. He only voiced Nergal in two episodes from the Grim and Evil special.
Then, he was voiced Martin Jarvis. He has been voicing him since Nergal Jr. was introduced and throughout the series.