It’s easy to get lost watching “Saturday Night”: Jason Reitman’s new film drops us backstage at a moment of maximum confusion — 90 minutes before the 1975 debut of a new NBC show called “Saturday Night.” At the center of all the hubbub is creator-producer Lorne Michaels (played by Gabriel LaBelle), who’s been the one constant at “S.N.L.” over most of the show’s 50 seasons. But what about all the other characters rushing about, wringing their hands over whether this show will actually make it to air? Here’s a guide:

The Original Cast

CHEVY CHASE AND GARRETT MORRIS These members of the original cast, known as the Not Ready for Prime Time Players, were hired as writers, not actors. Chase (played by Cory Michael Smith) had written for Alan King and the Smothers Brothers. As the anchor for “Weekend Update,” Chase, a master of mugging and pratfalls, became the show’s first breakout star and left in 1976 to embark on a film career. (He would return to guest host in 1978, when he reportedly got into fisticuffs with Bill Murray, the cast member who replaced him.)

Morris (Lamorne Morris, no relation) was a Broadway performer and a playwright with no improv or sketch comedy background. He was underused but became known for his impersonations of Sammy Davis Jr. and Tina Turner, as well as for yelling on “Weekend Update” (as the News for the Hard of Hearing interpreter). After the show, he stuck with TV comedy, appearing on sitcoms like “Martin,” “The Jamie Foxx Show” and “2 Broke Girls.”

GILDA RADNER, JANE CURTIN AND LARAINE NEWMAN The movie doesn’t try very hard to differentiate among the show’s female cast members — Gilda Radner, who died in 1989, Jane Curtin and Laraine Newman. But the three women had very distinct styles. Radner (Ella Hunt), a former member of Second City in Toronto, was the first performer Michaels signed and soon became a star beloved for her fragile, goofy style and characters like Roseanne Roseannadanna. It was her advocacy for fellow Second City veteran and ex-boyfriend Dan Aykroyd that persuaded Michaels to hire him.

Newman (Emily Fairn), a founding member of the Los Angeles improv troupe the Groundlings, knew Michaels from working together on a Lily Tomlin special. Her character Sherry the Valley Girl helped kick off a national fad mocking Southern California mall-speak. Newman’s expertise with accents and dialects paved the way for a post-“S.N.L.” career as a voice artist.

Curtin (Kim Matula), a member of the Boston improv group the Proposition, was one of the last cast members hired. She was often presented as the foil to more outrageous characters and helped ground many a sketch. As the first female anchor of “Weekend Update,” she was called upon to weather Aykroyd’s contemptuous catchphrase, “Jane, you ignorant slut.” After “S.N.L.,” Curtin became a sitcom star (“Kate & Allie,” “3rd Rock From the Sun”).