William Sloane Coffin Jr. (June 1, 1924 – April 12, 2006) was an American Christian clergyman and long-time peace activist.

His uncle was Henry Sloane Coffin, president of Union Theological Seminary and one of the most famous ministers in the United States.

His father, William Sloane Coffin, Sr. was an executive in the family business and president of the Metropolitan Museum of Art.

His mother, Catherine Butterfield, had grown up in the Midwest, and as a young woman spent time in France during World War I providing relief to soldiers, and met her future husband there, where he was also engaged in charitable activities.

William Sr.'s father, Edmund Coffin, was a prominent lawyer, real estate developer, and reformer who owned a property investment and management firm that renovated and rented low-income housing in New York.

William Sloane Coffin, Sr. died at home on his oldest son Edmund's eleventh birthday in 1933 from a heart attack he suffered returning from work.

After this, his wife Catherine decided to move the family to Carmel, California, to make life more affordable, but was able to do this only with financial support from her brother-in-law Henry.

The following year (when Edmund left for Yale University), William moved with his mother to Paris at the age of 15 to receive personal instruction in the piano and was taught by some of the best music teachers of the 20th century, including Nadia Boulanger.

The Coffins moved to Geneva, Switzerland, when World War II came to France in 1940, and then back to the United States, where he enrolled in Phillips Academy in Andover, Massachusetts.

While continuing his pursuit of the piano, he was also excited by the prospect of fighting to stop fascism and became very focused on joining the war effort.

Upon graduating in 1949, Coffin entered the Union Theological Seminary, where he remained for a year, until the outbreak of the Korean War reignited his interest in fighting against communism.

He joined the CIA as a case officer in 1950 (his brother-in-law Franklin Lindsay had been head of the Office of Policy Coordination, the political warfare arm of the CIA) spending three years in West Germany recruiting anti-Soviet Russian refugees and training them how to undermine Stalin's regime.

Along with others, he was a founder in the early 1960s of the Clergy and Laity Concerned About Vietnam, organized to resist President Lyndon Johnson's escalation of the war.

As chaplain at Yale in the early 1960s, Coffin organized busloads of Freedom Riders to challenge segregation laws in the South.

"[4] By 1967, Coffin concentrated increasingly on preaching civil disobedience and supported the young men who turned in their draft cards.

[5][6] Coffin was one of several persons who signed an open letter entitled "A Call to Resist Illegitimate Authority", which was printed in several newspapers in October 1967.

Coffin was a controversial, yet inspirational leader at Riverside, with sermon titles like "Abortion", "AIDS", "Homosexuality", and "Iran".

He and his wife lived in the small town of Strafford, Vermont, a few houses away from his brother Ned, until his death nearly two years later at age 81.