David Mixner, Fierce Fighter for Gay Rights, Is Dead at 77

David B. Mixner, a political strategist who played prominent roles in the anti-Vietnam War movement and in the arduous fight for gay rights, and whose decades-long influence with Bill Clinton spanned both eras, died on Monday at his home in Midtown Manhattan. He was 77.

The cause was complications of long-term Covid, said Steven Guy, a close friend.

Mr. Mixner, born three days apart from Mr. Clinton and raised in similar rural privation, met the future president when they were in their early 20s. He later arranged for Mr. Clinton to make the first public address by a major presidential candidate to a gay and lesbian audience, in 1992.

His political savvy was such that he was able to persuade California’s foremost conservative, Ronald Reagan, to oppose a 1978 state initiative to ban gay schoolteachers. The defeat of the measure was at that point the most significant win for gay rights in the country.

“When I met him when he was young,” Mr. Clinton said of Mr. Mixner in 1999, addressing an L.G.B.T.Q. group, “I thought I’d never met a person whose heart burned with the fire of social justice so strong.”

Mr. Mixner, the son of a farmworker in South New Jersey, dropped out of college to work as a political organizer, and in the late 1960s he seemed to be everywhere, including as part of Eugene McCarthy’s presidential campaign in 1968 and as a presence at the Democratic convention in Chicago that year. He was one of four national co-chairs of the Moratorium to End the War in Vietnam, a series of major protests in the fall of 1969.

Mr. Clinton met Mr. Mixner at a retreat for moratorium supporters on Martha’s Vineyard that year. The two men bonded during a walk on a beach, in part over their humble backgrounds, which set them apart from the upper-middle-class Ivy League students who were prevalent in the antiwar movement.