Magister Labrid was the first active Plumber to appear in the Alien Force series. He appeared to be a fish-like creature and it appeared that he was only able to stay alive in a water-like liquid that his suit was filled with.
Labrid first showed up in the first episode of Alien Force, because he thought Ben had stolen the Omnitrix. He tracked Ben down from the Rust Bucket all the way to where Gwen took karate lessons. When he first appeared, he was wearing an ID mask. He attacked Ben and Gwen while they were locked in the karate lessons building. Eventually, Gwen managed to capture him. After he explained himself, he apologized for attacking Ben, as he thought Ben was just some kid who stole the Omnitrix. He calls DNAliens air breathers, and appears to feel strongly about his job. He accompanied Ben and Gwen to a stakeout where a weapons trade, held by Kevin, between the DNAliens and the Forever Knights was happening. They managed to take down Kevin while the DNAliens and the Forever Knights escaped.
Kevin managed to lead them to the Forever Knight's base. He is mortally wounded during a battle with the Forever Knights while protecting Kevin. His dying wish was for Ben, Kevin and Gwen to complete their mission. Kevin takes his Plumber's Badge. Labrid evaporates during his death, with his Plumber suit empty.