The Gromble is the intimidating and strict headmaster of The Monster Academy, who demonstrates his tough love by belittling his students for poor scaring skills.

On one instance, he ate one of his students in one bite (although he spits him out after chewing him up), showing just how far he'll go to "punish" the poor students.

The Gromble calls his shoes "snuggle bears" and loves relaxing in his bed. Sometimes, he is referred to as "Gromble Sir" or "Mr. Gromble".

The Gromble's skin is a turquoise color. He has two blue flaps on his head resembling plane wings, a lumpy nose with a red hook at the tip, and some blue hair on his chin. His eyes are pink with black pupils. The Gromble has four feet with four red high-heel shoes on them. He has a blue goat tail and black gloves. The Gromble's belt is black with a gold or sliver buckle it seems to change on some episodes.