ZBrush model of a classic DooM style Baron Of Hell.

Looks like they got involved in some infighting and took a chunk out of a Hellknight with their teeth.
I've always thought that the eyes of a Baron of Hell (Hellknights and Cyberdemon too) are kinda like a cat's, so they don't really glow as such, just get bright and shiny when light hits them just right.

Model time: 4 hours, 5 minutes.
Paint time: 40 minutes.
Photoshop rendering time: 2 hours, 15 minutes.