My own interpretation of Fenrir, the giant wolf of Norse Mythology destined to arise at Ragnarok and devour the world.
The big mouth was largely inspired by this toy monster truck I used to have as a kid that, if you pulled a lever on its back, would split open to reveal a huge dragon-like mouth complete with teeth, tongue, and a fleshy palate and gums. Sort of an off-brand version of Hot Wheels' "Attack Pack" line.