Marvin Mitchelson, 76, the flamboyant and controversial divorce lawyer who pioneered the right to "palimony" with a landmark lawsuit against actor Lee Marvin in the 1970s and two decades later spent more than two years in federal prison for tax fraud, died Sept. 18 at a hospice in Beverly Hills, Calif. He had heart problems and skin cancer in recent years.

Since handling his first high-publicity divorce case in 1964 on behalf of actor James Mason's wife, Pamela, Mr. Mitchelson established himself as Hollywood's premiere divorce lawyer.

His list of clients included Sonny Bono, Tony Curtis, Mel Torme, Stephen Stills and Carl Sagan. Mr. Mitchelson, however, was known primarily as a "woman's lawyer," representing prominent clients such as Joan Collins, Bianca Jagger, Rhonda Fleming and Connie Stevens.

His most famous case was that of Michelle Triola Marvin, who had abandoned her nightclub singing career to be Lee Marvin's live-in companion and, after they broke up, demanded half of the $3.6 million the actor made during the six years they lived together. Although they were never married, she legally changed her surname to Marvin.

After Mr. Mitchelson filed Triola Marvin's breach-of-contract lawsuit, a Superior Court judge rejected the case in 1973, and 19 months later a California appeals court affirmed the dismissal.

The case then went to the California Supreme Court, which handed down its landmark ruling in late 1976 -- that unmarried, cohabiting partners could legally seek to share in a partner's property when they separated if the partners had express written or oral contracts; judges also could consider the partners' conduct to determine whether there was an implied contract.

Mr. Mitchelson later proudly called the state Supreme Court ruling "the worst setback for show business since John Wilkes Booth."

Despite Mr. Mitchelson's victory, the case wasn't over.

In 1979, after a 10-week trial in Los Angeles, a Superior Court judge ruled that there was neither an express nor an implied contract between the Marvins and that Triola Marvin was not entitled to anything.

But because the Supreme Court decision allowed judges to make monetary awards to live-in partners even when no express or implied contracts were found, the judge awarded Triola Marvin $104,000 to learn new job skills. In 1981, however, the state appeals court reversed the award.

Despite Mr. Mitchelson's courtroom loss, the high-profile case not only multiplied his business dramatically -- "I made millions" out of the publicity, he boasted to the Los Angeles Times in 1986 -- it made him one of the most famous lawyers in the world.

Mr. Mitchelson was born in Detroit and raised in Los Angeles. He was a graduate of the University of California at Los Angeles and Southwestern University School of Law.

He set up a law practice in Beverly Hills and landed a capital murder case in 1958 that resulted in the acquittal of his client. Assorted divorce, child custody and libel cases against tabloids followed.

In 1963, Mr. Mitchelson successfully argued a case before the U.S. Supreme Court that, along with another case, led to landmark decisions guaranteeing indigents the right to counsel at the trial court level and for appeals.

In 1964, he took over representing talk-show host Pamela Mason in her divorce from her British actor husband.

Two weeks before the trial, after Mr. Mitchelson subpoenaed about 40 of the Masons' prominent friends as prospective witnesses and made it known that he was prepared to disclose in court and to the media details of James Mason's private sexual matters, the actor settled out of court: He agreed to a $1.5 million settlement for Pamela -- the first divorce settlement to break the million-dollar mark.

By the early 1980s, Mr. Mitchelson had long been living a jet set lifestyle. He lived in an elaborately furnished Sunset Strip area mansion called "the Castle" and had a car collection that included, among others, two Rolls-Royces and a custom-made convertible once owned by Clark Gable.

Mr. Mitchelson sported $5,000 hand-tailored suits, was known to make more than a dozen trips to Europe every year and, although married, was frequently seen with an attractive young woman on his arm.

In 1988, the State Bar of California charged that in six separate instances, Mr. Mitchelson charged clients "unconscionable fees," failed to return unearned portions of financial retainers or performed his work badly -- all of which Mr. Mitchelson denied.

Mr. Mitchelson's life and career took a dive in 1993, when he was convicted and jailed for evading taxes on $2 million in income. The state bar suspended him, and he was forced into bankruptcy.

Mr. Mitchelson would recall later how he wept during his first day in federal prison in Fort Worth and his determination to survive the sentence.

He became a prison appellate attorney and helped gain freedom for three inmates. He helped others learn to read and write and started prison French and opera clubs.

When he was released from prison in 1997, Mr. Mitchelson worked as a consultant for other lawyers until his license was restored in 2000.

Survivors include his wife and son.

Marvin Mitchelson, shown with Joan Collins in 1987, represented or was involved in cases against many Hollywood stars and other celebrities.