The Gromble is the initial main antagonist later anti-hero of the popular cartoon show Aaahh!!! Real Monsters and although technically the headmaster of the school in which the main protagonists attend he is nevertheless the one most often responsible for making their lives miserable.
The Gromble is a very mean-spirited monster and a bit of a bully, taking delight in torturing his students both through physical and psychological abuse, though he seems to believe that his methods are justified as he leaves most of his truly wicked abuse for those who perform poorly at their "scare tactics".
Despite his bullying nature the Gromble is very learned and powerful, being one of the few monsters who can hear the Pool of Elders — the source of monster existence that is made of the very substance of fears (though Ickis can also do this, which is somewhat ironic considering Ickis is sweet-natured and lovable, a direct opposite of the cruel Gromble).
Although undoubtedly cruel and malicious it is worth noting the Gromble is actually doing his duty as a monster, seeking to train his students in the ways of scaring humans so that they may become "real" monsters. He is also capable of being pleasant towards those who do well in their tasks (for example he views Oblina as one of his best students and treats her accordingly).
The Gromble is a green-blue color. He has two blue flaps on his head, a red nose, and some blue hair on his chin. His eyes are pink with black pupils. Gromble has four feet with four red high-heel shoes on them. He has a blue tail and black gloves. Gromble's belt is black with a gold or sliver buckle it seems to change on some episodes.
- In the series' pilot episode, the Gromble's name is "Womble". His name was later changed to "Gromble" due to a British television series known as "The Wombles".
- There appears to be an inconsistency with Gromble's past. In both "Old Monster" and "Out of the Past", Gromble was shown to be a rookie monster during the 1920's. However, in "History of the Monster World", the Gromble is already a headmaster to Slickis and Horvak during the American Revolution.
- His age is unknown since he has been around since the American Revolution.
- It is hinted that Ickis will one day be Gromble's successor.
- The Gromble is similar to Mr. Burns. They are on-and-off masters of the heroes (Gromble: the trio, Burns: Homer Simpson), start out as antagonistic, though they don't mean to be, have clumsy toadies (Gromble: Snorch & Zimbo, Burns: Smithers) and are eventually usurped by the secondary but true villains. (Gromble: Simon the Monster Hunter, Burns: Sideshow Bob)
- He bears a physical resemblance to the Chief Blue Meanie.