Quinn was born in 1973 and raised in San Francisco, California, the son of Michael and Amanda Mallory. The driver's license shown in the episode "Summer of Love" indicates his birthday is January 24, but in the same episode, Wade says that Quinn is a Libra, which would put his birthday between September 23 and October 22.
Quinn was skipped ahead two grades in school at some point before 1984. He was bullied in junior high, and being skipped ahead two grades made him smaller and slower than his classmates. His father died in 1984. The week after his father's death, several students, including Rex Crandall, bullied Quinn at school, which ended in an incident where he hit Rex with a baseball bat. Quinn shattered Rex's kneecap, and Rex walked with a limp for the rest of his life. In the episode "The Guardian", on a world where events occurred as they did on Earth Prime twelve years ago, Quinn prevented history from repeating itself.
In "Summer of Love", Quinn tells to Arturo that he was starting quarterback in high school (indicating that despite being slower than his classmates in junior high, he became an athlete in high school). In the episode "Slide Like An Egyptian", Quinn meets his father in the afterlife while being used for life after death experiments. They discuss how they enjoyed playing American football together.
Invention of sliding
Quinn attended the fictional California University during the early 1990s to earn his master's degree in physics, specializing in superstring theory. In 1994, he invented a device that allows people to travel from one parallel dimension to another. Quinn referred to this technology as "sliding." On September 27, he went through the vortex with Wade Welles and Maximillian Arturo. Rembrandt Brown happened to be traveling in the area and was accidentally pulled into the vortex.
The four of them landed on a parallel world where San Francisco was in an ice age. They holed up in Rembrandt's car until a deadly tornado headed their way. Because of the way the sliding technology functioned, the group's only choices were to reset the timer and potentially lose the possibility to go home, or to wait for the timer to hit zero and go home then. Since the tornado was likely to kill them, Quinn had to reset the timer and lost the ability to return himself and the others home. For the next five years, Quinn and the others slid randomly to each world with a fixed amount of time on each one, hoping each slide will be the slide home.
In the fourth season premiere "Genesis", Quinn learned that he was not originally from Earth Prime, but that he was actually from Kromagg Prime, an Alternate earth where humans and Kromaggs coexisted until a civil war broke out between the two species. He learned that he was transported to Earth Prime when he was a baby and left with his parents' doubles. When his parents came back to get him, his adoptive parents were too attached to him so they hid Quinn, and Quinn was raised on Earth Prime. Quinn only learned this after he returned to Earth Prime after the Kromaggs had invaded two months prior. He also learned that he had a brother, Colin, who was transported to another alternate Earth as well.
The Unstuck Man
In late 1998 or early 1999, in the season five premiere "The Unstuck Man", Quinn and his brother Colin were unwillingly used in an experiment by Dr. Oberon Geiger to merge people and parallel worlds together. As a result of this experiment, Quinn was merged with a fraternal double of his who was referred to as "Mallory" (although his double's personality became dominant).
After Mallory was sliding for a while, the Sliders met back with Dr. Geiger in the episode "Eye of the Storm", and he attempted to unmerge Quinn from his double. Unfortunately, Dr. Geiger said that the two had been merged for too long and the only way to bring Quinn back would require killing Mallory. Rembrandt said that Quinn wouldn't want that, so Dr. Geiger ended the experiment and Quinn was presumed to be gone for good. But in "The Seer", Mallory told Quinn's mother that Quinn was still a part of him.
From 1994 to 1996, Quinn was very wide-eyed and eccentric, a quintessential nerd who was ever curious and somewhat naïve. Although his main interest was physics, Quinn had an encyclopedic knowledge of many things including dinosaurs, Texas history, baseball, and football.
Quinn seems to suffer from an inferiorty complex that drives his need to succeed. It could also account for joining the football team in high school (despite probably starting off smaller than his teammates) and his need to rescue people.
Because of the teasing and bully he endured as a child, Quinn dislikes bully of any kind. This often leads to his jumping in to save people without thinking (especially women who quickly take advantage of his good hearted nature). Professor Arturo dubbed this as "Mr. Mallory's penchant for the quixotic rescue."
In late 1996, he became less quirky and more of an action hero. The death of Professor Arturo saw Quinn change even furthur, turning him into a hard man who alone shouldered the burden of getting the group home.
- In the episode "The Breeder", Quinn says, "I thought the military draft was bad on our world," after learning about a requirement on an alternate Earth for young adults to be organ donors.
- Quinn often expresses opposition to the death penalty.
- It seems he does not like to be referred to as professor.
- Quinn is shown to be a communist supporter and a fan of Robin Hood along with hating monarchism and being a radical democrat to the extent of terrorism and thievery in "The Prince of Wails"
- Wade Welles: Quinn and Wade were close friends, working at the Doppler Computer Store. Wade had a crush on Quinn, something that he was too oblivious to notice for some time. Both "Last Days" and "The Weaker Sex" (where Quinn even goes so far as to not deny being Wade's boyfriend when asked) saw an advancement in their relationship but by "Luck of the Draw" things had stalled and in "Obsession" the Professor had to counsel Quinn over his jealousy of Wade dating another man. In the end, both were too shy and too occupied by situations they were thrown into to fully act upon their feelings.
- Maximillian Arturo: Being Quinn's professor, it wasn't always easy for Arturo to accept his student surpassing him. Whatever resentment Arturo felt for Quinn was one sided and largely unexpressed because Quinn looked up to Arturo who often doubled as a surrogate father. Quinn's relationship with Arturo filled a big void, and Quinn was very hurt when Colonel Angus Rickman murdered Arturo. Arturo death opened Quinn's eyes to the dangers of sliding and made Quinn a harder man.
- Rembrandt Brown: Initially, Rembrandt was at odds with Quinn, being the only one not to consent to sliding. The bitterness continued for a short duration, but dulled as Rembrandt gained respect for Quinn. The two became close friends, like brothers, though they still occasionally harbored conflicting views. Rembrandt gave Quinn the nickname "Q-Ball."
- Maggie Beckett: Quinn might have been attracted to Maggie. In "The Exodus, Part Two", Dr. Stephen Jensen (Maggie's husband at the time) accused Quinn of having a romantic interest in Maggie, saying "I see the way the two of you look at each other and I don't like it." Quinn told Dr. Jensen that he felt Maggie is just someone he had to put up with, but Dr. Jensen did not believe him. In "The Breeder", Wade remarked to Quinn, "You have a thing for her [Maggie]?" which Quinn denied. At the end of "This Slide of Paradise" they share a very intensive goodbye kiss. Later episodes ("Virtual Slide" and "Slide by Wire") revealed that they had not pursued a relationship during their three months of solo slides. It also revealed that while Maggie has feelings for Quinn any feelings he may have had for her have cooled. However in "Roads Taken", Quinn and Maggie were married in a "bubble universe" that existed only for the two of them, revealing that Quinn did have some feelings for Maggie.
- A double of Quinn appears in the pilot episode. This double helps Quinn solve the equation that will allow him to slide. The double later appears in "The Other Slide of Darkness, where it is revealed that he was also responsible for giving sliding technology to the Kromaggs.
- In "Fever", a double of Quinn is Patient Zero for the Q virus. He is later cured thanks to Professor Arturo's "invention" of penicillin.
- In "Eggheads", Quinn impersonates his double to find the double's sliding system only to discover his double does not have a sliding system and is probably in hiding after running out on $1 million debt owed to the mob.(Double not seen on camera)
- In "Into the Mystic", a double of Quinn is The Sourcer, a reclusive mogul who has cornered the market on goods being sold on his adopted earth. He assist the sliders in getting home but they do not realize it and slide out without ever knowing.
- In "The Young and the Relentless" Quinn's double, who is married to Wade's double, is an education software designer/executive who is murdered by his wife. (Double is only scene as body in the swimming pool)
- In "The Guardian" a twelve-year old double of Quinn appears in a world where time runs slower so they land in a world that looks like 1980s.(Double is played by a young actor)
- In "The King is Back", Quinn is sentenced to death for tagging- an act committed by his double. (Double not seen on camera)
- In "Dead Man Sliding" Quinn is sentenced to death for acts believed to be committed by his doubles. It is revealed that his double, a petty thief, was framed and he decides to help the sliders break Quinn out of jail before Quinn is executed.
- In "World Killer" Quinn's double is responsible for sliding the entire population of his planet to an alternate earth.
- In "My Brother's Keeper", Quinn runs into his double who is accidently blind during an experiment and Quinn is mistaken for his double's clone. (Three versions of Quinn Mallory were seen on camera)