Update
Steve Skubinna, in the comments:
Growing up, I knew MacMurray form My Three Sons and the Disney films. Fatherly or avuncular, the epitome of decency.I put this comment in the post for a couple of reasons. First, I agree 100%; MacMurray was an incredibly versatile actor, starring in dramas, comedies, romantic movies and even westerns. And in the second place, the comment gives me an excuse to post the following video clip of a scene from the hilarious, but shamefully underappreciated 1945 screwball comedy, Murder, He Says, in which MacMurray plays the role of a poll-taker who is trying to track down a colleague who went missing out in the sticks somewhere. Without having seen more of the movie than is represented by this scene, you don't really have the full context of what's going on, but the slapstick stuff is funny in its own right.
I think the first time I saw him play a less that savory character was as Keefer in The Caine Mutiny. That was disturbing. Next was as Jack Lemmon's smooth but amoral boss in The Apartment. Wow. Then Double Indemnity. Golly, but that guy could play anything! I now believe that he was his generation's most underrated actor. Incredible ability to break whatever expectations you had from his previous work.