When an arrogant, aging, iconic comedian of yesteryear met an overly confident, young up-and-coming comic beginning to make his mark on the biz, it was pretty much a given that their worlds would clash. And in Jason Reitman’s “Saturday Night” — a “based-on-a-true-story” account of what happened 90 minutes before the 1975 debut of “Saturday Night Live” — that is exactly what happened between Milton Berle and Chevy Chase when they met. It was less a passing of the baton and more of a “mine is bigger than yours.”

J.K. Simmons plays Berle, a superstar of his time as a funny man on radio and TV who ultimately became known as Mr. Television, to Cory Michael Smith’s Chase in the biographical comedy-drama. When Reitman approached Simmons about the role, the Oscar winner says he was intimidated but was assured they weren’t looking for an impressionist to tackle the role, but rather...