Ghostbusters 

Before becoming a movie star, Rick Moranis was known as a master improviser. He was well known for being an ad-lib king, with many of his roles still being fan favorites even though he hasn’t acted in a couple decades. His portrayal as Louis Tully, the perfect depiction of an uncool guy in Ghostbusters, is one of the reasons the movie is such a classic.

At one point, he is holding a party for many of his clients, instead of his friends. The line most people may remember is when the monster is about to burst from the coat room, and Louis says, “Ok, who brought the dog?” It was revealed later that the majority of the scene was completely improvised, mostly by Moranis.