Terrance Mephesto is a member of the fourth grade class and rival to the main boys. He debuted in "An Elephant Makes Love to a Pig" and has made occasional cameos since.
Although Terrance has never been seen inside the fourth grade classroom outside of his debut episode, he frequently appears in the background. In "Lice Capades", he is seen in a different line to the main class; as it is known that there is at least one other fourth grade classroom, this may explain his absence from Mr. Garrison's class.
Terrance wears a purple jacket with a black neck tie and yellow suspenders attached to orange pants. His hair and eyebrows are dark brown and he has prominent chin. His eyebrows are of a peculiar shape, being jagged, unusually thick and forming a monobrow. He still has his unusual eyebrows in current seasons, but they can only be seen when he's scared or angry, they also seem to have gotten smaller.
Terrance appears to have an abrasive personality, actively seeking out conflict in "An Elephant Makes Love to a Pig". He also appears to be incredibly arrogant and self-centered; when his father warns him about the danger his clone poses to the people of South Park, he exclaims "They're all stupid anyway!". Terrance also disparagingly calls Kyle a plebeian, showing his arrogant demeanor.
In "An Elephant Makes Love to a Pig", Terrance is shown to be Dr. Alphonse Mephesto's son, although he never appears with his father again, nor is he mentioned as such. Since his mother never appears, it is possible he lives with her. Terrance appears to have a good relationship with his father, who happily helps his son with his science project of cloning a human.
It is not known what relationship Terrance has with Kevin, Dr. Mephesto's constant companion.
Terrance is accompanied almost constantly by Bill and Fosse in "An Elephant Makes Love to a Pig". The pair are assumed to be part of Terrance's cabal, but they have yet to appear as a group since. Terrance was quite clearly the brains of the group; Bill and Fosse did nothing but follow him around and remark that things were "pretty gay".
In his debut episode, Terrance, Bill and Fosse appeared as a group rivaling the boys, betting that they could clone a human before the boys could crossbreed an elephant and a pig.
- Terrance was scheduled to appear in "South Park: The Stick of Truth" but was cut out of the game, it is unknown what his role would be in the game. His friend icon can be found in the game files. He had the same eyebrow models from Damien on his icon in an old game build. It is also called "Terrence" in the game files.
- He still has his unusual eyebrows in current seasons, although they rarely appear. The last time he was seen with them was in "The Problem with a Poo".
- Despite his deceased status, Terrance continues to make background appearances following his alleged death ("Mecha Streisand") and confirmed death (The Fractured but Whole). It is unknown whether this is simply an oversight on the animators' part or if he was revived off screen.
Although Terrance faded from prominence very quickly, he still makes occasional background appearances.
- "An Elephant Makes Love to a Pig" - Bets that he can clone a human faster than the boys can create a pig-elephant crossbreed.
- "Conjoined Fetus Lady" - Seen in dodgeball team.
- "Tweek vs. Craig" - Seen watching Tweek and Craig fight.
- "Chinpokomon" - Seen at the toy store, participating in the Chinpokomon fad with the other children.
- "Hooked on Monkey Phonics" - Seen at the school dance.
- South Park: Bigger, Longer & Uncut - Seen as a member of La Resistance.
- "World Wide Recorder Concert" - Seen in the background.
- "Trapper Keeper" - Seen in class.
- "Scott Tenorman Must Die" - Seen laughing in the background.
- "The Biggest Douche in the Universe" - Briefly seen on the playground as Rob Schneider rides a hobby elephant in the Rob Schneider is Kenny trailer.
- "Fat Butt and Pancake Head" -
- "The Jeffersons" - Seen in Michael Jefferson's house.
- "Quest for Ratings"
- "Ginger Kids" - Appears in Ginger Kids' cells.
- "Mystery of the Urinal Deuce" - Terrance, along with Timmy, Bill, and Pip are seen in the audience when Mr. Mackey is giving his speech, though he does not speak.
- "With Apologies to Jesse Jackson" - Three Terrance clones are seen in the background at the school assembly. One of them is white-haired.
- "The List" - Seen with Brimmy.
- "Breast Cancer Show Ever" - Seen watching the climactic fight.
- "The F Word" - Seen in the background at the school assembly.
- "Faith Hilling" - Seen in the memeing class with the other 4th Grade students.
- "Jewpacabra" - Seen at the Easter egg hunt.
- "Butterballs" - Seen in the background at the school assembly.
- "Sarcastaball" - Seen in the background in the locker room.
- "A Scause For Applause" - Seen in the background in the school hallways.
- "Member Berries" - Cameo
- "Douche and a Danish" - Seen in the battle between the girls and the boys.
- "Oh, Jeez" - Seen at the school assembly.
- "The Problem with a Poo" - Seen in the school assembly.
- "Band in China" - Seen at the Autumn Fest.
- "Let Them Eat Goo" - Seen in the assembly.
- "Tegridy Farms Halloween Special" - Seen at the school assembly.
- "Board Girls" - Seen at the school assembly.
It was revealed that he died during the episode "Mecha-Streisand". The kids thought he was going to be revived by Dr. Mephesto, but he instead told them that he's going to give Terrance's corpse more asses so he can finally rest in peace.