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So many stars have appeared on long-running drama “Law & Order” that it’s become a litmus test, says its creator.

Dick Wolf said during a 92nd Street Y panel, “If you go to the theater and you run across an actor who does not have a ‘Law & Order’ credit, it means they just got off the bus, or he really sucks.”

Everyone from Bradley Cooper to Frank Langella, to Whoopi Goldberg, Martin Short and Carol Burnett have shown up in guest roles, among endless others.

Former cast member Jeremy Sisto said during the talk that his favorite guest star was Adam Driver.

“He was a very strange dude, like sweet but just had a lot going on,” Sisto recalled.