Stephen Mo Hanan, a vibrant performer who sang arias and other music as a busker in San Francisco before playing Kevin Kline’s lieutenant in the acclaimed 1981 Broadway production of “The Pirates of Penzance” and three felines in the original Broadway cast of “Cats,” died on April 3 at his home in Manhattan. He was 78.

Gary Widlund, his husband and only immediate survivor, said the cause was a heart attack.

At his audition for “Cats,” Mr. Hanan (pronounced HAN-un) told Andrew Lloyd Webber, the composer, and Trevor Nunn, the director, that he had spent several years singing and accompanying himself on a concertina at a ferry terminal at the foot of Market Street in San Francisco.

“As a matter of fact, I’ve brought my concertina,” he recalled telling Mr. Nunn in an interview with The Washington Post in 1982. “He said, ‘Give me something in Italian.’ Well, I’ve never had a problem with shyness. I sang ‘Funiculi, Funicula.’”

Mr. Hanan was ultimately cast in three parts: Bustopher Jones, a portly cat, and the dual role of Asparagus, an aging theater cat, who, while reminiscing, transforms (with help from an inflatable costume) into a former role, Growltiger, a tough pirate, and performs a parody of Puccini’s “Turandot.”

In an entry about the second day of rehearsal, he described an assignment from Mr. Nunn: to “pick a cartoon cat we know of, withdraw to ourselves and prepare a vignette of that cat, then return to the circle and each in turn will present.”

He continued: “I choose Fritz the Cat,” the Robert Crumb character, “making a pass at some kitty. Watching the others is a gas — people’s individualities are beginning to emerge.”

He and another cast member, Harry Groener, were both nominated for the Tony Award for best featured actor in a musical. They both lost; the tap dancer Charles (Honi) Coles won for “My One and Only.”

In the years following “Cats,” Mr. Hanan’s many roles included Moonface Martin in “Anything Goes,” at the Guthrie Theater in Minneapolis; the double role of Voltaire and Dr. Pangloss in “Candide,” at the Huntington Theater in Boston; and another dual role, Mr. Darling and Captain Hook, in “Peter Pan,” on Broadway and on tour. He also portrayed the villainous innkeeper Thenardier in “Les Miserables” in London.

In 1999, Mr. Hanan created a stage role of his own: Al Jolson, the popular vaudevillian who performed in blackface, sang on Broadway and starred in “The Jazz Singer,” the pioneering sound motion picture. “Jolson & Co.,” which Mr. Hanan wrote with Jay Berkow, was staged Off Broadway, at the York Theater Company.

Al Jolson “was pure id,” Mr. Hanan, who bore a physical resemblance to him, told Harvard magazine in 2002, when the show was revived at the Century Center for the Performing Arts in Manhattan. “He didn’t censor himself, neither his joy nor his rage. With Jolson you can be completely over the top; you have to be. His personality demands that kind of size.”

“Jolson & Co.” recreates a 1946 radio interview with Barry Gray as a way of looking back on his remarkable life. Mr. Hanan sang many of the songs Mr. Jolson was known for, including “Swanee” and “California, Here I Come.”

Reviewing the show in New York magazine, John Simon praised Mr. Hanan’s performance as “mostly impersonation but, as such, unbeatable.” He added, “On top of the Jolson looks, the incarnator has absorbed all the vocal, facial, and kinetic mannerisms as if he had stolen the man’s very soul.”

Mr. Hanan was born Stephen Hanan Kaplan on Jan. 7, 1947, in Washington. His mother, Lottie (Klein) Kaplan, was a high school English teacher; his father, Jonah Kaplan, was a pharmacist.

While attending Harvard College, Stephen performed in theatrical productions at the Loeb Drama Center and with the Hasty Pudding Club. He acquired the nickname Mo on a trip to Bermuda during college, after a friend, the future Broadway librettist John Weidman, observed that his outfit made him look like “some guy named Mo who cleans cabanas in the Catskills,” Mr. Hanan told the website TheaterMania in 2002.

After graduating in 1968 with a bachelor’s degree in English literature, he studied for a year at the London Academy of Music and Dramatic Art on a Fulbright fellowship.

Back in New York, he had difficulty landing roles, so in 1971 he moved to San Francisco, where he lived on a commune and spent six years singing for money, mostly at the ferry terminal, which earned him enough to spend winters in Mexico and Guatemala.

Once, outside the stage door at the War Memorial Opera House in San Francisco, he encountered Luciano Pavarotti, who had just performed in Verdi’s “Un Ballo in Maschera,” and summoned the nerve to sing for the great tenor.

“I raced to the money note and he, exclaiming ‘Che voce d’oro’ — or ‘What a golden voice’ — beckoned me over amid applause,” Mr. Hanan wrote in an unpublished essay.

After returning to New York again, he landed small parts in New York Shakespeare Festival productions of “All’s Well That Ends Well” and “The Taming of the Shrew” in Central Park in 1978. (Around that time, he dropped his surname and began using his middle name instead, because there was another actor with a similar name.)

In 1980, the director Wilford Leach cast him as Samuel, the second in command to Mr. Kline’s Pirate King, in the Shakespeare in the Park production of the Gilbert and Sullivan comic operetta “The Pirates of Penzance,” which also starred Linda Ronstadt. Mr. Hanan stayed with the show when it moved to Broadway in 1981.

Rex Smith, who played Frederic, the male romantic lead, said in an interview that Mr. Hanan “embodied all that was required to be the Pirate King’s lieutenant, and for that you had to stand and deliver every night — if you’re not going to be keelhauled.”

In 2006, Mr. Hanan moved up in rank to play the Major-General in a Yiddish-language version of “Pirates” (called “Di Yam Gazlonim!”), put on by the National Yiddish Theater Folksbiene at the Jewish Community Center in Manhattan (now the Marlene Meyerson JCC Manhattan).

Allen Lewis Rickman, the director, of that show recalled that Mr. Hanan did not know Yiddish and had to learn his lines phonetically.

“He was quite a character and very entertaining, one of those people who you know is a real pro,” Mr. Rickman said in an interview. “He had a clownish streak — that was his first instinct — but not in a scene-stealing way.”