CHICAGO — As soon as Charna Halpern walked backstage at the iO theater here, the 20 or so comedians in the room got quiet, their eyes focused on her. They were about to perform for a full house, but she was the only audience that mattered.

Every year, Ms. Halpern, 63, the co-founder and owner of the iO, sees hundreds of performers do five minutes before she picks 15 to present to the producers of “Saturday Night Live” in a summer showcase. Getting to this final 15 is the golden ticket of Chicago comedy, and there are many stories of unknowns, like the current cast members Cecily Strong and Vanessa Bayer, cashing it in for stardom. Ms. Halpern, wearing a blue shirt with slits down the arms and comfortable slippers, told the comics to not be nervous, then asked for questions. Silence. Walking out the door, on her way to her front-row seat, Ms. Halpern described what she just saw with characteristic bluntness: “Young and afraid.”

The name Del Close is better known, and Second City here and the Upright Citizens Brigade in New York get the lion’s share of attention, but Ms. Halpern is the overlooked powerhouse of improv, the woman who with little fanfare has played a major role in shaping the current comedy boom. She provided a launching pad to some of comedy’s most famous names — she introduced Tina Fey to Amy Poehler, who took her first improv class from Ms. Halpern — and helped transform improvisation from a marginal art form into a bustling business (with five theaters in New York alone devoted to it and thousands of students taking classes around the world) and cultural force that rivals stand-up.

Adam McKay, the director and former improviser who thanked Ms. Halpern when he won an Oscar for “The Big Short,” compares her to the producers who brought hip-hop to the mainstream. “In the early days, it was an art in the neighborhoods, but you needed entrepreneurs like Russell Simmons to provide a framework for it to explode,” he said. “That’s what Charna did for improv.”