[Allison] Jones began her career with the two-beats-and-a-punch-line sitcoms of the nineteen-eighties, but, in working with Feig and the director Judd Apatow, she was required to try something revolutionary: find comedic actors who, more than just delivering jokes, could improvise and riff on their lines, creating something altogether different from what was on the page.

In the process, Jones has helped give rise to a new kind of American comedy. In 1999, she cast Seth Rogen, James Franco, and Jason Segel in the critically acclaimed, poorly watched teen series “Freaks and Geeks.” The show, created and written by Feig and produced by Apatow, was a coming-of-age story set in the suburban Michigan of Feig’s youth. Jones won the show’s only Emmy, for her casting. Several years later, she met with a young, sweaty Jonah Hill, who was desperate for an introduction to Apatow. She told Apatow that Hill was weird and hilarious. That sufficed; Apatow expanded a cameo part for Hill in “The 40-Year-Old Virgin,” as an odd but lovable eBay customer. Two years later, Hill was cast with Michael Cera in “Superbad,” a raunchy teen comedy that Apatow produced. It was left to Jones to find their nerdier-than-thou friend McLovin. Jones posted notices seeking high-school students in L.A. After seeing thousands of candidates, she caught a glimpse of a camera-phone head shot sent in by a sixteen-year-old named Christopher Mintz-Plasse. She called the director, Greg Mottola, and excitedly said, “I think I found McLovin; he’s like Dill from ‘To Kill a Mockingbird.’ ” Jones told me, “You could tell he was a kid who probably had seen the inside of a locker.” Since then, Mintz-Plasse has starred in six movies.