Alex Hassilev, a multilingual, multitalented troubadour and the last original member of the Limeliters, one of the biggest acts of the folk revival of the early 1960s, died on April 21 in Burbank, Calif. He was 91.

His wife, Gladys Hassilev, said the cause of his death, in a hospital, was cancer.

Before Beatlemania gripped America’s youth in 1964, the country fell in love with the tight harmonies and traditional arrangements of folk music — and few acts drew more adoration than the Limeliters, a trio made up of Mr. Hassilev, Glenn Yarbrough and Lou Gottlieb.

Mr. Hassilev played banjo and guitar and sang baritone, not only in English but in French, Portuguese, Spanish and Russian, all of which he spoke fluently. His bandmates were equally brainy: Mr. Gottlieb had a doctorate in musicology and Mr. Yarbrough once worked as a bouncer to pay for Greek lessons.

Urbane and witty, they packed coffeehouses and college auditoriums with a repertoire that mixed straight-faced folk standards like “The Hammer Song” and cheeky tunes like “Have Some Madeira, M’Dear,” “The Ballad of Sigmund Freud” and “Charlie the Midnight Marauder.”

At their height, between 1960 and 1962, the Limeliters were playing 300 dates a year and recording an album every few months, two of which — “Tonight in Person” (1960) and “The Slightly Fabulous Limeliters” (1961) — reached the Billboard Top 10.

“The Limeliters have a certain musical and verbal finesse which places them above and beyond their many contemporaries,” The Los Angeles Times wrote in 1961.

Alexander Hassilev was born on June 11, 1932, in Paris, the son of Jewish immigrants from Russia, Leonide and Tamara (Rudd) Hassilev. With the threat of war with Germany mounting, the family emigrated to New York in 1939, where Mr. Hassilev worked as a civil engineer.

Alex proved a diligent, brilliant student, breezing through high school and entering Harvard after serving in the Army. But he reacted against what he saw as the university’s Yankee elitism and, after a year, transferred to the University of Chicago. Even there he felt constrained by academic life; eager to try his hand at acting, he returned to New York.

He studied at the Neighborhood Playhouse, learned the guitar and fell in with the emerging folk scene around Greenwich Village. He had a small but memorable role as a guitarist in Roger Corman’s 1959 horror-comedy “A Bucket of Blood.”

Around the same time he met Mr. Yarborough, who was visiting from Aspen, Colo., at a party. Mr. Yarborough had a regular gig playing at a cafe there called the Limelite. Mr. Hassilev, an avid skier, soon joined him.

With the Limelite as their home base, the pair was soon appearing at venues along the West Coast. While playing at a coffeehouse in Los Angeles, they caught the eye of Mr. Gottlieb, who had recently finished his dissertation on 15th-century liturgical music and was arranging pieces for the Kingston Trio, another popular folk group.

The three men began jamming together, and in 1959 they took their act on the road. They booked several nights at the hungry i, a popular venue in San Francisco; when the owner balked at putting all three of their names on the marquee, they decided to call themselves the Limeliters.

The trio’s success was swift. They signed with Elektra Records and released their first album in 1960. In between touring and appearing on television, they recorded a string of commercial jingles, including “Things Go Better With Coke.”

But their tight harmonies were not matched offstage, where their constant squabbling earned them the nickname the Bicker Brothers. After a plane crash in Utah in 1962 left them shaken (but mostly unharmed), Mr. Yarbrough left. The trio formally broke up in 1965.

Mr. Hassilev recorded a solo album and rekindled his interest in acting. He had a few successes, including a guest spot on the TV comedy “Get Smart” and a role in the 1966 comedy “The Russians Are Coming, the Russians Are Coming!” playing one of the titular Russians alongside two other folk musicians who were transitioning to acting: Theodore Bikel and Alan Arkin.

But he had a hard time breaking away from his fame as a folk singer. He set up a studio in the basement of his West Hollywood home, and for several years worked as a record producer.

His first marriage, to Ginger Stanjer, ended in divorce. He married Gladys Rios in 1976. Along with her, he is survived by his son, David, two grandchildren and three great-grandchildren.

Mr. Hassilev reconvened the Limeliters several times in the late 1960s and ’70s and then permanently in 1981, with Mr. Yarbrough dropping in and out of the lineup. After Mr. Gottlieb died in 1996, Mr. Hassilev brought in new performers, many of them veterans of the 1960s folk scene. Mr. Yarbrough died in 2016.

Mr. Hassilev retired from the Limeliters in 2006, though he continued to play with them occasionally, and the band remains active today. Though they never returned to their 1960s popularity, they continue to play to large and enthusiastic audiences.

“In order to remain popular, you have to outlive your competition,” Mr. Hassilev told The Charleston Daily Mail of West Virginia in 2005. “It makes me feel good to be in this field. It makes me feel clean.”