Ken Osmond, who helped create a TV archetype while playing the two-faced teenager Eddie Haskell on “Leave It to Beaver,” kissing up to authority figures before getting into trouble and putting down his young peers as soon as the adults looked away, died May 18 at his home in Los Angeles. He was 76.

The cause was complications from chronic obstructive pulmonary disease and peripheral arterial disease, said his wife, Sandra Osmond.

With his curly blond hair, flair for high jinks and obsequious way with teachers and parents, Mr. Osmond’s Eddie was an indelible television character for viewers of “Leave It to Beaver,” which ran in syndication for decades and practically defined the image of middle-class boyhood and the all-American family during the Eisenhower era.

Broadcast by CBS and then ABC, the show ran for six seasons, from 1957 to 1963, and starred Jerry Mathers as the impressionable Theodore “The Beaver” Cleaver, whose older brother, Wally, played by Tony Dow, was pals with Eddie. The series presented a slightly less sanitized version of childhood than its TV contemporaries, in large part because of Mr. Osmond’s character — a mischievous prankster whose name became shorthand for generations of duplicitous bullies.

Eddie skipped class, encouraged the Cleaver boys to watch a scary movie instead of the parent-approved “Pinocchio” and tricked the Beaver into reciting a Spanish phrase meaning, “You have a face like a pig.” He also changed his tune as soon as an adult entered the picture: “Wally,” he declared in a typical tirade, “if your dumb 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.”

The character’s ingratiating manner was not entirely effective — “I just don’t trust a 13-year-old boy that’s that polite,” Barbara Billingsley’s Mrs. Cleaver says in one episode — and at times he seemed more troubled than villainous. “If you can make the other guy feel like a goon first,” he says, “then you didn’t feel so much like a goon.”

But his antics made him a template for countless misbehaved television characters, with “Simpsons” creator Matt Groening recalling that he would “vibrate with happiness” whenever Eddie appeared on-screen. “Bart Simpson is the son of Eddie Haskell,” he said in an interview for the “Make ’Em Laugh” book and documentary “flash forward 30 years later.”

Mr. Osmond was cast for a single “Leave It to Beaver” episode at age 14 but went on to appear in 95 more. “I have always said that he was the best actor on our show,” Mathers said in a tribute, “because in real life his personality was so opposite of the character that he so brilliantly portrayed.”

Like other child actors, Mr. Osmond found it difficult to distance himself from the role that made him a star. He appeared on shows including “The Munsters” and “Petticoat Junction” but struggled to find work after “Leave It to Beaver” went off the air, running a charter helicopter service and eventually joining the Los Angeles Police Department.

“I was very much typecast. It’s a death sentence,” Mr. Osmond told a radio interviewer in 2008. “I’m not complaining because Eddie’s been too good to me, but I found work hard to come by. In 1968, I bought my first house, in ’69 I got married, and we were going to start a family and I needed a job, so I went out and signed up for the LAPD.”

Ribbed by fellow officers for his portrayal of Eddie, he grew a mustache to disguise himself, worked as a motorcycle cop and was shot three times by a suspected car thief while on patrol in 1980. Two of the bullets struck his protective vest, and the third was deflected by his belt buckle. Days later, he was nearly shot again when a bullet whizzed past his head during a foot chase.

Mr. Osmond said that he had depression as a result of the shootings and spent days in isolation without speaking to his wife or children. He ultimately retired from the force and said that his disposition really improved only after he returned to the role of Eddie Haskell, playing an older version of the character for a 1983 TV movie that spawned a cable series, “The New Leave It to Beaver.”

Midway through its four-season run, he told United Press International: “I’m on top of the world now.”

Kenneth Charles Osmond was born in Glendale, Calif., on June 7, 1943. His father was a studio carpenter and prop maker, and his mother began taking Eddie to auditions when he was 4. He and his brother, Dayton, made their film debuts in the Mayflower movie “Plymouth Adventure” (1952) and were taken to classes in diction, ballet, fencing and martial arts.

He had his first speaking part at 9 in the Robert Wise drama “So Big” (1953) and appeared in shows including “Circus Boy,” “Annie Oakley” and “Lassie” before being cast in “Leave It to Beaver.” The show was not a major hit during its initial run but became increasingly popular while in syndication, with a New Times magazine contributor later linking Mr. Osmond’s character to the countercultural movement that emerged after the show ended.

“Those of us who started out as normal, healthy American kids and ended up being branded aberrant by society needed an Eddie Haskell, someone whose very existence is an insult to Ward Cleavers everywhere,” future NBC president Brandon Tartikoff wrote in the magazine, referring to the Beaver’s strait-laced father.

In joining the police, Tartikoff added, Mr. Osmond had effectively repudiated that character. “We can no longer depend on Ken Osmond,” he wrote. “He grew up to be Ward Cleaver.”

Mr. Osmond spent years trying to dispel myths about Eddie Haskell, who was rumored to have been played by rock star Alice Cooper and porn star John Holmes (who billed himself as “Eddie Haskell” in several X-rated movies).

Mr. Osmond played Eddie’s father in a PG-rated feature film, “Leave It to Beaver” (1997), and occasionally guest-starred in television shows such as “Happy Days.” When he returned to the role of Eddie in “The New Leave It to Beaver,” he was joined by his two real-life children, Eric and Christian Osmond, who played his kids on the show.

They survive him, in addition to his wife of 50 years, the former Sandra Purdy, and two grandsons.

Mr. Osmond maintained friendships with “Leave It to Beaver” cast members including Mathers, with whom he sometimes appeared at grocery-store openings, and Frank Bank, who played Eddie’s friend Clarence “Lumpy” Rutherford and became a stock-and-bond broker, serving as Mr. Osmond’s accountant and financial adviser.

“We had a family,” Mr. Osmond told Fox News host Bill O’Reilly in 2007, recalling the environment on set. “It really was and still is.”