Basement-Dweller: He still lived with his mother while finishing college. He still had his own room, but converted his basement into a makeshift laboratory and spent most of his free time down there.
Brilliant, but Lazy: In the pilot, he passes up the chance to correctly answer a difficult question (despite Arturo yelling at him) because it didn't interest him. On the other hand, he took the time to read Arturo's papers that weren't assigned for class because their contents did.
"The Dream Masters" reveals she was once robbed at knife-point, giving her a fear of knives and of being cut. She also has a problem with snakes, though apparently got over it by the time of "Slither."
Last Name Basis: If the others don't address him as "Professor," then they do this.
Missing Mom: According to "Season's Greedings," his mother died during a World War II bombing. While Word of God confirms that the Arturo that said this was the double from "Post Traumatic Slide Syndrome," their two worlds were described as so similar that the real Arturo likely experienced similar events.
Secretly Dying: Introduced in "The Guardian," where Quinn finds out and is sworn to secrecy. Rembrandt would find out in "The Last of Eden."
So Proud of You: He's not one to get emotional, but his admiration for Quinn always came through.
Every teacher goes through life hoping just once he'll have a student like you.
Spot the Imposter: In "Post-Traumatic Slide Syndrome," the Sliders find themselves faced with two Arturoes each claiming to be theirs. The Sliders themselves have trouble figuring out who is who and Word of God ultimately confirmed what fans long suspected: the wrong one slid with them.
Put on a Bus to Hell: In "The Unstuck Man," Colin was made unstuck and left involuntarily sliding from one dimension to the next. At first, there was concern that Colin didn't survive, but he was generally treated as still alive and in need of help. By the end of the season, however, the characters acknowledged that Colin may really be dead, but it was nonetheless left ambiguous.
Smarter Than You Look: Colin is rather naive, but only because he came from a less advanced world. He is nonetheless quite intelligent, adapting rather well to modern technology and figuring things out for himself.
Flip Personality: Mallory emerged as the dominant personality, but in "The Unstuck Man" and "Applied Physics," Quinn's personality and memories periodically broke through. By the end of "New Gods for Old," however, Mallory could no longer feel Quinn.
I Owe You My Life: He is weary of Dr. Geiger, but acknowledges that without him, he'd still be in a wheelchair.
Last Name Basis: Mainly because Maggie was incapable of calling him "Quinn," and then everybody picked it up. Even Diana, who knew him before Season 5's events.