In an age that worships fame and wealth it’s inevitable, I suppose, for most people to remember the celebrities who took classes at ImprovOlympic: Chris Farley, Andy Dick, Mike Myers. But what makes that talent factory remarkable–and partly accounts for its longevity–is how egalitarian it is, churning out scads of strong, funny, committed performers. Most ImprovOlympic alums are not famous. Or they’re famous only among other professionals: Brian McCann, who writes for Conan O’Brien (and occasionally performs on his show), is respected by his fellow comedy writers, and teacher-director Susan Messing casts a long shadow in Chicago’s improv world and almost no shadow outside it. But in the long run, these artists have had more influence on American comedy than any out-of-control celebrity. Moreover, some of the best improv I’ve seen has been created by people too raw, spontaneous, and confrontational to get hired by SNL. For ImprovOlympic’s two-day 20th-anniversary fest, a number of teams will reunite–among them Blue Velveeta (McCann’s and Messing’s team) and the Family (many of whom were founding members of the Upright Citizens Brigade)–and other alums will perform. ImprovOlympic founder Charna Halpern promises that Del Close will make a posthumous appearance. Athenaeum Theatre, 2936 N. Southport, 312-902-1500. August 3 and 4: Friday-Saturday, 8 PM. $25.