Sid Caesar, a virtuoso mimic and mime whose television shows in the 1950s dominated the viewing habits of tens of millions of Americans and who helped make sketch comedy an art form during television’s infancy, died Feb. 12 at his home in Beverly Hills. He was 91.

A family spokesman, Eddy Friedfeld, confirmed the death to the Associated Press. No details were immediately available.

In a career spanning seven decades, the tall, brooding and comically uninhibited Mr. Caesar became one of the greatest live wires of television history. His artistry with dialect gibberish made him phenomenally famous on “The Admiral Broadway Review” (1949), “Your Show of Shows” (1950-54), “Caesar’s Hour” (1954-57) and “Sid Caesar Invites You” (1958), but the strain of acting in live comedy programs every week for nearly 10 years and a long addiction to alcohol and barbiturates nearly destroyed him.

A mercurial genius, he by turns supervised, inspired and physically threatened a team of actors and writers of nearly unparalleled comic talent, including Mel Brooks, Neil Simon, Woody Allen, Carl Reiner and Larry Gelbart. They were credited with pioneering a freewheeling comic approach later imitated by such sketch programs as “Saturday Night Live,” “Rowan & Martin’s Laugh-In” and “The Carol Burnett Show.”

“What Marlon Brando was to dramatic acting, Sid Caesar was to comedy,” Time magazine critic Richard Corliss wrote. Caesar’s cast and crew, Corliss added, summoned a “wit, drive, sophistication and narrative shapeliness that put to shame all that came after.”

In 1949, when few Americans had seen professional actors or comedians in person, tens of millions of viewers with newly purchased television sets watched “The Admiral Broadway Review” and found themselves delighted with Mr. Caesar alongside slapstick comedian Milton Berle and tiny, rubber-faced actress Imogene Coca.

Mr. Caesar was so successful that the next year he got his own program, “Your Show of Shows,” 90 minutes of live comedy each Saturday night. The variety series, co-starring Coca, Reiner and Howard Morris, drew 60 million viewers, but it was done on a demanding schedule that was the equivalent of producing a new Broadway show each week.

“Your Show of Shows” featured scripted and improvisational comedy, satirical sketches, parodies, monologues, musical guests and production numbers, as well as Mr. Caesar's inimitably warped characters.

They included the Professor, a German-accented scientist who in fact knows nothing; the pretentious “cool jazz” saxophonist Progress Hornsby; Somerset Winterset, a blowhard storyteller modeled on Somerset Maugham; and, with Coca, an uproariously mismatched married couple called Charlie and Doris Hickenlooper.

“With Imogene, I was always the overpowering bully husband,” Mr. Caesar said. “I was big and strong. But Imogene always led me along by the nose. I was the guy who thought he was a bully, but the audience knew what I was.”

Mr. Caesar satirized film genres from silent film melodrama to contemporary westerns. In one bravura sketch, he and his cast played mechanical figures in a Bavarian town clock who become increasingly haywire with each strike of the hour.

Another of his signature routines, “The $5 Date,” was inspired by his dates with Florence Levy, whom he married in 1943.

Mr. Caesar acknowledged the influence of Charlie Chaplin, Buster Keaton, W.C. Fields, and Laurel and Hardy in his pantomime routines, but he was especially known for his foreign-language gibberish. He perfected the double talk as a child by listening to the dialects of the émigrés who patronized his parents’ 24-hour luncheonette in Yonkers, N.Y. In truth, Mr. Caesar admitted, the only language he could speak was English.

His shows’ grueling schedules took a toll. A hulking man (6-foot-1, more than 200 pounds), he had the stamina for the job but also an unpredictable temper and excessive eating and drinking habits. He consumed a fifth of Scotch whisky each night, he said in his 2003 memoir “Caesar’s Hours,” in an effort to fall asleep.

Mr. Caesar’s tantrums and the raucous antics and fights among the writers and comedians were the basis for Simon’s 1993 play “Laughter on the 23rd Floor” and inspired the 1982 film “My Favorite Year.”

In his 1982 autobiography, “Where Have I Been?,” Mr. Caesar acknowledged that he did not recall entire years of his life. According to New York Times critic Frank Rich, who reviewed the book, “At the height of his insanity, Mr. Caesar would rip sinks out of the bathrooms in his Great Neck, L.I., family manse, or dangle the young Mel Brooks out of an 18th-story hotel window. . . . In 1978, having long since lost most of his friends, Mr. Caesar spent four months entirely in bed, secretly ordering in beer whenever his wife turned her back.”

Colleagues and fans were long aware of his problems. In 1956, Mr. Caesar wrote about his emotional struggles and subsequent psychoanalysis in an article in Look magazine. It was a bold move at a time when alcoholism and other addictions among celebrities were generally hidden from the public.

“On stage, I could hide behind the characters and inanimate objects I created,” he wrote. “Off stage, with my real personality for all to see, I was a mess. . . . I couldn’t believe that anyone could like me for myself.”

Isaac Sidney Caesar was born Sept. 8, 1922, in Yonkers to Jewish immigrants. He said his brother Dave first recognized his comedic talent when the 11-year-old Mr. Caesar was playing the saxophone at a school concert, darting about the stage to escape the glare of the spotlight so he could read the music.

As a teenager, he played in dance bands and orchestras in resorts in the Catskill Mountains, where he was also enlisted as a straight man for comedians. Mr. Caesar audited several courses at New York’s Juilliard music school, but producer Max Liebman, who worked in theater and later TV, convinced him that his skills at comedy would take him further.

While Mr. Caesar was still serving in the Coast Guard during World War II, Liebman put him in a variety show, “Tars and Spars” (later made into a 1946 film). He went on to book the young comedian into other nightclubs and stage productions, including the 1948 Broadway musical revue “Make Mine Manhattan.”

New York Times theater critic Brooks Atkinson wrote that the “imaginative and clever” Mr. Caesar was “the most original item in the program. An amiable product of the local habitat, he can mimic anything from a subway vending machine to a dial telephone or a taxi driver, and rush through it with tremendous speed.”

Mr. Caesar was making $3,500 a week, more than the mean annual income in the United States, when Liebman arranged for him to appear in Berle’s “Texaco Star Theater” and then with Coca in “The Admiral Broadway Revue.”

The series was tremendously successful — too successful for Admiral, a maker of television sets and home appliances. Admiral could not keep up with the demand for new TVs and decided to build a new factory rather than continue sponsoring the show. The series was canceled after 19 weeks.

Undaunted, and believing that Mr. Caesar was worth headlining, Liebman and NBC President Pat Weaver decided to create a new 90-minute Saturday-night program, “Your Show of Shows.” It premiered in February 1950 and brought Mr. Caesar two Emmy Awards for his acting.

In 1962, he returned to the Broadway stage in “Little Me,” with a book by Simon, music by Cy Coleman and lyrics by Carolyn Leigh. Mr. Caesar played eight parts that required 32 costume changes — among them, a French musical hall singer, a German director in Hollywood and a free-spending Slavic prince — and earned a Tony nomination for best actor in a musical.

He appeared in several theatrical movies over the years, including roles as a dentist who cannot stand pain in Stanley Kramer’s all-star comedy “It’s a Mad Mad Mad Mad World” (1963) and as an overzealous football coach in the 1978 musical “Grease.” He was also cast by Brooks in as a studio chief in “Silent Movie” (1976) and as a caveman in “History of the World: Part I” (1981).

Despite years in psychotherapy, Mr. Caesar continued to fight addiction throughout his life. In the late 1970s, he blacked out during a stage production of Simon’s “Last of the Red Hot Lovers” and forgot his lines.

Even after his psychological breakdown, Mr. Caesar continued to be in demand, and his credits included television series, TV movies, variety specials and more than 50 appearances on episodic shows. He earned Emmy nominations for his guest roles on the sitcoms “Love & War” and “Mad About You.”

He also made 15 stage appearances, including playing a speaking role as a drunken jailer in a 1987 Metropolitan Opera production of Johann Strauss II’s “Die Fledermaus.”

His wife, Florence, died in 2010 after 67 years of marriage. Survivors include three children. Complete information about survivors was not available.

For all his other achievements, Mr. Caesar was forever identified with his pathbreaking TV work in the 1950s. He and others involved on those early shows described their efforts as a madcap experiment limited only by their imagination. Live television, Mr. Caesar said, required a commitment to comedy that could be agonizing at times.

“I remember a satire we did on ‘High Noon,’ ” he told the New York Times in 1982. “The townspeople were supposed to abandon me and return their deputy badges to me by pinning them on my chest. I was supposed to have a sponge inside my shirt. But I didn’t have time to change. So they kept coming, saying, ‘Sorry, Sheriff,’ and pinning on the badges. After it was over, I went backstage, and somebody said, ‘Hey, you did real good pain takes.’ I told him the pain was for real.”