4 young monks of diverse ethnic backgrounds join forces in a fight against malevolent evil in Kids' WB's Xiaolin Showdown. The series lasted three seasons, stretched out further by reruns to about five, and remains a fan favorite long after the series' cancellation.
Jack Spicer (Danny Cooksey, ex-Diff'rent Strokes) was supposed to be a primary villain in season 1, but was more or less comedy relief because he was a bumbling goof. He'd eventually switch sides twice in the course of the series' run, but I couldn't take him too seriously.
Unfortunately, today, the series languishes in the vaults at WB, due to the internal squabbling between Warner Bros. Animation and Cartoon Network over rights fees, among other petty things.
Xiaolinshowdown11 (naturally) uploaded the series opener.