Duffin, who also acted on TV and in films, died April 23 of complications from heart surgery at UCLA Medical Center, said his daughter, Ruth.
"Inside each Irishman is a one-man show trying to get out," Duffin wrote in The Los Angeles Times in 1978.
His performance piece was the tale of anti- English rebel Behan, whom The Times once described as a "playwright-raconteur-professional drunk." When Behan died at 41 in 1964, a member of the British press wrote: "Too young to die. Too drunk to live."
In 1975, Duffin won a Los Angeles Drama Critics Circle Award for his performance in what was eventually known as "Brendan Behan: Confessions of an Irish Rebel."
He also wrote the script, basing it on Behan's writings, and liked to point out that he had a passing acquaintance with Behan, who also hailed from Dublin.
"Duffin as Behan: Mad, Magic Irishness" read the headline on a 1976 Times review of the show, then at the Cast Theater in Hollywood. It praised his "quivering portrayal of the inner Behan" and said it brimmed with Irish "native wit and tenderness."
Duffin spoke with a thick brogue and delighted in his resemblance to Behan. He often said they shared "the same map-of-Ireland face."
Born Feb. 26, 1931, Duffin started his career as a teenager, singing in Irish pubs.
In the early 1960s, he moved to Canada, where he spent five years with an all-Irish theatrical company and recorded albums as an Irish folk singer.
While hosting a revue, he began working on his one-man show, which took him five years to hone. After opening in Toronto and playing other cities, he brought it to Los Angeles. He would go on to present it thousands of times.
Onstage, he also appeared in "The Dead" by James Joyce and "The Importance of Being Irish," which Duffin wrote.
He had roles in about 35 movies and television shows. Often, he was cast as the bartender, including in the films "The Departed" and "Titanic." He also was a regular on "City," a short-lived 1990 CBS sitcom.
A longtime resident of Redondo Beach, Duffin often wrote letters to The Times on a variety of subjects. In 1977, he ended a plea to Hollywood to hire "real" Irish actors by saying, "All we want is a fair shake of the 'schtick.' "
In addition to his daughter Ruth, Duffin is survived by daughters Laura, Linda and Susan, and two grandchildren.