Brick Flagg is the star quarterback of the school football team. He once thought Kim liked him, due to a fraudulent story Ron wrote for the school newspaper, as seen in the episode "All the News". Despite being cast in the role of the stereotypical "dumb jock", Brick does manage to avoid being cast in a "school bully"-type role. In fact, aside from a confrontation he had with Japanese transfer student Hirotaka in the episode "Exchange", Brick typically does not make it a point to throw his weight around and actually seems to be a genuinely nice, if slow-witted, guy.
For most of the second and third seasons, Bonnie Rockwaller was his on-again/off-again girlfriend, but it didn't seem to be a genuine attachment, as in Kim Possible Movie: So the Drama, he showed some interest in Kim's friend, Monique. By "Homecoming Upset", he had apparently dumped Bonnie, now that he was in college. During that episode, Ron called him and tried to convince him to get back together with Bonnie, to which Brick informed Ron that he had no intentions of resuming a relationship with Bonnie. Ron also realized during their conversation that college had actually made Brick much smarter and that he had completely moved on from anything related to high school.
In Kim Possible: A Sitch in Time, a bald and fat future version of Brick Flagg was seen. He looks similar to the future Beast Boy seen in the Teen Titans episode "How Long is Forever".
Brick was initially stated to be only a year older than Kim and Ron, according to a press release, but he seems to be much older than that, because at the beginning of Ron's senior year Mr. Barkin stated that, "after seven years, Brick Flagg graduated last June", although it is uncertain if seven was the total number of years he was in high school―indicating he was held back for three years―or the number of times he failed to graduate―meaning he was in high school even longer; none of which addresses if he was held back in any of the other grades.
In the episode "Car Trouble", he was in the same Driver's Ed. class as Kim, Ron, and Bonnie. He kept crashing into the cones, rather than try to avoid any of them. He was also in the same class as Kim, Ron, Monique, and Bonnie in the episode "Partners", he was partnered with Bonnie, which may have been when they began dating. There's also an apparent continuity error between "Royal Pain" and "Homecoming Upset" since in the first episode Brick is running for class president against Kim, but in the latter he's stated to have graduated before Kim.
- Royal Pain (first appearance)
- All the News
- Ron the Man
- Kim Possible Movie: So the Drama (final appearance)
- Ill Suited (mentioned)
- Homecoming Upset (mentioned)
- Brick Flagg is voiced by Rider Strong, who previously co-starred in Boy Meets World with Will Friedle, Ron's voice actor.
- Brick Flagg bears a resemblance to Hun from Teenage Mutant Ninja Turtles 2003 series.
- After he left Middleton High, his football jersey number, 7, was passed to Ron Stoppable.