The younger brother of talk-show psychiatrist, Dr. Marvin Monroe, Mervin was the prime subject for all of Marvin's early experiments. After Marvin sent 2000 volts through his electric blanket in an attempt to cure Mervin of his bedwetting problem, Mervin ran away from home for good. He learned his tattooing art while participating in a failed CIA plot to discredit Castro by tattooing a smiley face on Fidel's forehead. His most tragic "skin art" experience centered on Tattoo Annie, who not only broke Mevin's heart but also had it tattooed on her butt. He has a woodpecker named Pokey.
In "Simpsons Roasting on an Open Fire", Bart decides to get a tattoo and is able to trick the Tattoo Parlor Guy into believing he is old enough to get a tattoo. He was able to almost complete the tattoo before Marge pulled Bart away. He got a heart and the word "MOTH" on Bart's arm; all he needed to complete it were the letters "ER".
- He has one known relative in Springfield, Marvin Monroe.
- He slightly resembles and is possibly an early version of the Comic Book Guy due to them both being overweight, both having a blue shirt and both having a tiny bit of facial hair.
- His beard is actually a tattoo.
- Episode – "Simpsons Roasting on an Open Fire"
- Episode – "Flaming Moe's"
- Episode – "A Star is Burns" (archive footage)
- Episode – "Home Sweet Homediddly-Dum-Doodily"
- Episode – "Sweets and Sour Marge"
- Episode – "The Wandering Juvie"
- Episode – "The Food Wife" (Grand Theft Scratchy cover)
- Video game – The Simpsons Game (Grand Theft Scratchy cover)
- Comic story – Box Office Bingo