Coffin had been suffering from congestive heart failure and had been under the care of a hospice, said his daughter, Amy Coffin.
"He was out in the sun. Everybody was talking and then he was gone," Amy Coffin said. "Physically he was pretty debilitated but spiritually he was not."
William Sloane Coffin was immortalized in the "Doonesbury" comic strip when its creator, fellow Yale graduate Garry Trudeau, blended his character with that of a Trudeau roommate, who became a priest, dubbing the fictitious character "Rev. Sloan."
Coffin gained prominence in the 1960s as an outspoken advocate for civil rights and against the Vietnam War. He joined a group of civil rights activists known as the freedom riders and was arrested several times at demonstrations against segregation. He became a leader of the group Clergy and Laity Concerned About Vietnam, which engaged in civil disobedience including offering sanctuary in churches and synagogues to draft resisters.
"Bill's voice was part of a chorus of conscience for a nation dealing with issues of poverty, war, disarmament, racism and bigotry," the Rev. Frederick J. Streets, Yale's current chaplain, said Wednesday. "He distinguished himself by rising above and emerging out of his own background of privilege to speak on behalf of the poor."
In awarding Coffin an honorary doctorate in 2002, Yale praised its former chaplain, saying, "You changed the shape of college chaplaincy and inspired a generation of young people to challenge injustice."
He continued his activism after leaving Yale in 1976 and moving on to become minister of the Riverside Church in New York City. There he broadened his agenda to working on issues of peace, nuclear disarmament, poverty, homelessness and protecting the environment. But he was criticized by some in the congregation as too attentive to his social agenda, at the expense of pastoral work and management of the church.
He retired from Riverside in 1987 to Vermont, but continued traveling the country lecturing on issues.
He traveled to North Vietnam during the war with that country and to Iran during the hostage crisis there, bringing harsh criticism from some quarters. To those who questioned his patriotism, Coffin often replied that the true patriot is one who maintains "a lover's quarrel" with his country.
In 1967, Coffin and other prominent activists including Dr. Benjamin Spock took more than 1,000 draft cards gathered from young men at rallies in Boston and other cities and presented them to officials at the Department of Justice in Washington. Coffin, Spock and three other protest leaders were arrested and convicted for advising men on avoiding the draft; the convictions were overturned on appeal in 1970.
Born to a wealthy New York family in 1924, Coffin served in World War II, then resumed study at Yale as a political science student in the late 1940s, but developed an interest in theology and philosophy and enrolled in the Union Theological Seminary.
The outbreak of the Korean War rekindled his interest in fighting communism, and he served three years in the CIA.
He then enrolled in Yale's Divinity School, receiving his bachelor's degree and being ordained a Presbyterian minister in 1956. He spent a year each as chaplain at Phillips Andover Academy and Williams College. At Williams, he became controversial through his activism against fraternities that discriminated against blacks and Jews.
He was appointed chaplain at Yale in 1958, where he served 18 years.
Coffin's longtime friend, historian and activist Howard Zinn, said he'll miss Coffin's humor. He recalled a speech in which Coffin spoke to a group of students about what to do after graduation.
"He said, 'Remember this: Even if you win the rat race, you're still a rat," Zinn said.