Without Groucho Marx, there would have been no Woody Allen. Groucho (and the rest of the Marx Brothers) pioneered the modern New York Jewish brand of humor that, after World War II, became one of the defining sensibilities of American comedy. In the '60s, that legacy was taken up by Allen, who frequently referenced the Marx Brothers both implicitly and explicitly in his films. Allen's most famous movie, "Annie Hall," even name-checks Groucho in the opening monologue of the film.
But for a time, Woody and Groucho were not on good terms. After striking a friendship in 1961, there was radio silence between the two for several years after Groucho failed to respond to a letter. In 1967, word got back to Groucho that Woody was hurt by the lack of communication, and Groucho sent him an apology letter that only he could have penned.
The letter read in part:
March 22, 1967
Dear WW:
Goodie Ace told some unemployed friend of mine that you were disappointed or annoyed or happy or drunk that I hadn't answered the letter you wrote me some years ago. You know, of course, there is no money in answering letters -- unless they're letters of credit from Switzerland or the Mafia. I write you reluctantly, for I know you are doing six things simultaneously -- five including sex. I don't know where you get the time to correspond.
Your play, I trust, will still be running when I arrive in New York the first or second week in April. This must be terribly annoying to the critics who, if I remember correctly, said it wouldn't go because it was too funny. Since it's still running, they must be even more annoyed. This happened to my son's play, on which he collaborated with Bob Fisher. The moral is: don't write a comedy that makes an audience laugh.
Groucho goes on to tell a whimsical tale of receiving gifts from his aunt that were sabotaged by his brother Chico. He concludes with an invitation to meet up with Allen the next time they both found themselves in Manhattan.
They seemed to stay on good terms for the rest of their lives. When Groucho died in 1977, Allen reprimanded TIME Magazine for their short obituary. (For what it's worth, Woody Allen is currently the age Groucho Marx was when that letter was sent: 76.)
Check out Letters of Note to read the entirety of the letter.