Context

This classic line is spoken by Rick Blaine, played by Humphrey Bogart, in the film Casablanca (1942) directed by Michael Curtiz.

At the end of Casablanca, Rick Blaine has lost everything. Rick stays behind in Casablanca and lets the beautiful Ilsa board a plane and escape. Nazi Major Strasser tries to stop them, but Rick shoots him, all in front of Captain Louis Renault.

When the police arrive, Louis has the opportunity to turn Rick in, but he doesn't, saying "Round up the usual suspects." (Keyser Söze, perhaps?) As the two men walk away, Rick tells the Captain, "Louis, I think this is the beginning of a beautiful friendship." Louis is no Ilsa, but he'll do.

Where you've heard it

You've probably heard it misquoted in a variety of ways, from "This could be the beginning of a beautiful friendship" or "I think this is the start of a beautiful friendship." This quote signifies the start—er, beginning—of a friendship that is not only beautiful, but unlikely as well.

Additional Notable References

• It's been referenced on Breaking Bad and Veep. 
• This line was cut from the theatrical release of The Exorcist. (A beautiful friendship between a priest and Satan?!)

Pretentious Factor

If you were to drop this quote at a dinner party, would you get an in-unison "awww" or would everyone roll their eyes and never invite you back? Here it is, on a scale of 1-10.

Everybody could use a new friend. We added a point for quoting a black-and-white movie.