Mr. Stuart is a character from the 1982 movie Grease 2.
Mr. Stuart was new substitute teacher, replacing Mr. Spears aftermental exhaustion relapse, along with taking too many pills.
While speaking with Principal McGee in the hallway, Ms. Mason walked by, and they were smitten with each other. Apparently, the attraction was mutual, and Mrs. McGee picked up on that, flustered by Ms. Mason's flirtatious behavior.
Unfortunately, after he walked into the classroom and introduced himself, all of the students got up from their chairs and walked out of the classroom.
His shining moment came in Biology class teaching about Reproduction. First, he asked what time was best for a woman to conceive, meaning when was the best time for a woman to be fertile. He skimmed the class roster, and smirked, singling out one of the supposed "cool crowd", Davey Jaworski, causing Louis DiMucci to snicker at the fact that Davey had ZERO knowledge of women. The question was bounced from Davey to Johnny Nogerelli, to Goose McKenzie then Louis, who answered: "At night." They weren't getting very far so he started at the beginning.
Mr. Stuart had the rare distinction of being the only teacher at Rydell who had ever had a major role in a musical number (although Mrs. Murdock could be seen dancing in the background of Greased Lightnin'). However, very soon the class got out of hand. Just after the `Reproduction' number, Principal McGee called him out, telling him that the students' bodies were fully developed, but not their minds.
Some months later, at the June Moon Talent Show he and Ms. Mason had to suffer through some mediocre performances, namely Martin Misner and his "Red-Hot Accordion". He reacted to the music as if sedated, nearly nodding off, but ultimately he remained awake, especially since Ms. Mason was sitting right next to him.
At the Lani Kai Lani Luau, he and Ms. Mason formed a relationship, as they were seen first in the middle of the Pool of Enchantment, in a flower-adorned raft. They were seen in close-up, about to steal a quick kiss, as they swished their pom-poms in front of them, concealing their actions.
It can be assumed that Mr. Spears retired after "rescued" from the Pool of Enchantment, and Mr. Stuart took over as a full-time permanent teacher.