He is a substitute teacher who has had much experience teaching inner city kids for over 20 years. He quickly gets upset with his students when he incorrectly pronounces their names and no one responds. He returned in Season 3, thinking that the students he was teaching were lying about going to take their club photos and instead going to the "club".
Two commonly known aspects to his rage are breaking his clipboard in half over his knee, and when Aaron (the kid who commonly attracts Mr. Garvey's wrath) tells Mr. Garvey something around the end of the skit, Mr. Garvey slides everything off of his desk, yells at Aaron (A.A. Ron), and then sends him up to Principal O'Shaughnessy (Oh-Shag-Hennesey)
He is known for using modern black culture phrases, such as "You feel me?" and "For real", as well as contractions like "Y'all" and "Ain't", he also uses esoteric words like "chicanerous" and "churlish"