When Gary joins the fourth grade class, Mr. Garrison tells the class about Gary's past. Gary previously lived in Utah, where he was a straight-A student and captain of the wrestling team. He has been in two toothpaste commercials.
Gary has wavy blond hair parted on the right side and swept in a smooth style. He wears an open turquoise jacket, a white collarless shirt, light blue jeans, and black shoes. He also wears a gray belt with a metal, D-style belt buckle, and black shoes.
Gary’s personality appears to be shaped largely by his family and religion, Mormonism. He is friendly, outgoing, and optimistic. When he is teased and bullied by other students at school, he doesn't appear to be bothered by it. For example, in "All About Mormons", Eric Cartman introduces himself to Gary as "Ura Fag." Rather than acting upset or embarrassed, Gary laughs. Later, when Stan threatens to “kick [his] ass,” Gary promises not to fight back and even hopes that they can be friends someday.
Although he’s friendly and forgiving, Gary is not a pushover. When Stan refuses to be Gary’s friend because of his religion, Gary responds with a very thoughtful speech about how proud he is to be Mormon and what it has done for him. The speech ends with: "All I ever did was try to be your friend, Stan. But you were so high and mighty that you couldn’t just look past my religion and be my friend back. You’ve got a lot of growing up to do, buddy. Suck my balls."
Gary’s parents are very supportive and nurturing, and he loves and respects them for it. He has a very close relationship with his parents.
Gary has four siblings: Mark, Jenny, David, and Amanda Harrison. Gary has a strong relationship with all of his siblings. They never fight and genuinely enjoy spending time together. All five siblings play musical instruments, and perform a song for their parents and Stan Marsh in "All About Mormons".
After approaching Gary with the intention of "kicking his ass", Stan realizes that Gary is actually a very nice person. Gary and Stan start hanging out together, though Stan became a little reluctant to participate in this developing acquaintance, as the other boys, notably Cartman, began teasing him for “being in love.” Finally, after hearing the story of The Book of Mormon, Stan decides that Mormonism is ridiculous, and he no longer wants to be Gary’s friend over his religion.
- "All About Mormons" — Gary moves to South Park from Utah and joins Mr. Garrison’s fourth grade class. He is briefly Stan’s friend and tells him about Mormonism.
|style="background: #Template:Color1; color:#FFF; text-shadow:#000 .1em .1em .1em; padding-left:20px; border-radius:5px 5px 0px 0px;" align="center" colspan="2"|South Park families|
Broflovski Family | Cartman Family | Marsh Family | McCormick Family | Stotch Family | Biggle Family | Black Family | Cotswolds Family | Donovan Family | Gueermo Family | Hakeem Family | Harrison Family | Mephesto Family | Stevens Family | Tenorman Family | Testaburger Family | Tucker Family | Tweak Family | Valmer Family |
|style="background: #Template:Color1; color:#FFF; text-shadow:#000 .1em .1em .1em; padding-left:20px; border-radius:5px 5px 0px 0px;" align="center" colspan="2"|Harrison Family|