Stewart R. Mott, a philanthropist whose gifts to progressive and sometimes offbeat causes were often upstaged by his eccentricities, like cultivating a farm with 460 plant species (including 17 types of radishes), a chicken coop and a compost pile, atop his Manhattan penthouse.
Mr. Mott’s philanthropy included birth control, abortion reform, sex research, arms control, feminism, civil liberties, governmental reform, gay rights and research on extrasensory perception.
His political giving, often directed against incumbent presidents, was most visible. In 1968, he heavily bankrolled Senator Eugene McCarthy’s challenge to President Lyndon B. Johnson. Four years later, he was the biggest contributor to Senator George McGovern, the Democratic presidential nominee.
After the 1974 campaign finance law outlawed exactly the sort of large political gifts in which Mr. Mott specialized, he joined conservatives to fight it as an abridgement of free expression. They argued that limits on contributions given independently of a candidate’s organization were unconstitutional. In 1976, the Supreme Court agreed, while keeping other parts of the law.
Mr. Mott seemed to relish poking his finger in the eye of General Motors, a company that his father, Charles Stewart Mott, helped shape as an early high executive. Mr. Mott broke into politics in 1968, when he used newspaper advertisements to pledge $50,000 to the as-yet-nonexistent presidential candidacy of Gov. Nelson A. Rockefeller of New York. Mr. Mott paid most of the early legal fees for a 1976 suit that ultimately caused former Vice President Spiro T. Agnew to repay kickbacks ($147,599 plus interest) that he had been accused of receiving when he was governor of Maryland.
He was the son of Charles Stewart Mott and the former Ruth Rawlings, Mr. Mott’s fourth wife. He finished his education at the Columbia University School of General Studies, earning two bachelor’s degrees, one in business administration and one in comparative literature, as well as a Phi Beta Kappa key. His philanthropy began when he returned to Flint and started the city’s first branch of Planned Parenthood. He then traveled the nation on behalf of Planned Parenthood.
For years, Mr. Mott was a highly publicized eligible bachelor. When The Washington Post reported that he had slept with 40 women over an eight-month period, he issued a correction, saying the number was actually 20.
In 1979, he married Kappy Wells, a sculptor. They divorced in 1999. He is survived by a son, Sam, of Santa Fe, N.M., and a sister, Maryanne Mott, of Santa Barbara, Calif., and Montana.