Fox News confirmed the news on Monday. He was 76 years old.
The actor starred in the series from 1957 to 1963 after landing the role at just 14 years old. Osmond's Eddie was the best friend of Tony Dow's Wally Cleaver, big brother to Jerry Mathers' Beaver Cleaver. He constantly kissed up to adults and kicked down at his peers, usually in the same scene, and was the closest thing the wholesome show had to a villain. Viewers of all ages loved to hate him.
The role of Eddie in season one of “Leave It to Beaver” was supposed to be a one-off guest appearance, but the show's producers and its audience found him so memorable he became a regular, appearing in nearly 100 of the show's 234 episodes.
Check out his top moments from the show below:
Eddie appeared polite but would make insulting comments to the Cleavers.
Eddie Haskell: Gee, your kitchen always looks so clean.
June Cleaver: Why, thank you, Eddie.
Eddie Haskell: My mother says it looks as though you never do any work in here.
Eddie oftentimes tried to ditch Wally's younger brother, Beaver.
Eddie Haskell: Wally, if your d--b brother tags along, I'm gonna — oh, good afternoon, Mrs. Cleaver. I was just telling Wallace how pleasant it would be for Theodore to accompany us to the movies.
Eddie would try to hide his bad intentions by pretending to be a gentleman when the Cleavers were listening.
Eddie Haskell: [Beaver thinks he isn't going to graduate from eighth grade] Hey, that's tough, kid. Let me think. Maybe I can help you figure a way out of this.
Wally Cleaver: Listen, Beav. At this point, I don't think you want to be taking advice from Eddie.
Eddie Haskell: Are you kidding? I've been in an out of every kind of trouble there is in school.
He was always trying to tempt Wally.
Eddie Haskell: Hey Wally, nobody's home. Let's call up some girls and pretend we're talent scouts.
June Cleaver: [Enters the room.] Hello, Eddie.
Eddie Haskell: Oh. Hi, Mrs. Cleaver. Gee Mrs. Cleaver, your hair looks real pretty today.
June Cleaver: Well, you should know Eddie, being a talent scout.
And he made a political jab every once in a while.
Eddie Haskell: Not me! Your father doesn't like me.
Wally Cleaver: Why would you say that?
Eddie Haskell: On account of the way he looks at me when he opens the door. Sometimes I think he'd be happier to see Khrushchev standing there.
Fox News' Mariah Haas and The Associated Press contributed to this report.