Grunt is the name given to a type of very large, strong, and not notably intelligent creature that inhabits Limbo. Thus far, the purple Grunt has been seen in many episodes. He was killed, eaten, and face-fucked in episode 206: New Heaven by the angels who were looking to kill the large dominant fauna of Limbo.
Basic Grunt appears in two known types. First is the common purple Grunt, and in episode 203: Income Parable, a red version appeared being ridden by the Angry Aristocrat.
Large Grunt also appears in two types, both only appearing in episode 203. They come in green and purple.
MechaGrunt is a large, robotic version of the Grunt. It is the largest type of Grunt yet seen and the only one to speak. Even though it is a robot, it speaks in a caveman-esque dialect. Speaking to Alpha, it said "You know what? Me trust you. Me do it out of solidarity." when asked to kick Simon into the sea.