Walter Leslie AuCoin (/oʊˈkɔɪn/ oh-KOYN; born October 21, 1942) is an American politician. In 1974 he became the first person from the Democratic Party to be elected to the U.S. House of Representatives from Oregon's 1st congressional district, since it was formed in 1892. The seat has been held by Democrats ever since.

AuCoin's 18-year tenure—from the 94th United States Congress through the 102nd—is the sixth-longest in Oregon history. In his career, AuCoin took a prominent role in abortion rights, local and national environmental issues, multiple-use management of federal forests, and national security. During the presidency of Ronald Reagan, he wrote the ban to stop Interior Secretary James Watt's plan to open the Pacific Outer Continental Shelf to oil exploration. AuCoin was an early advocate of diplomatic relations with the People's Republic of China and arms control with the Soviet Union, and a critic of U.S. support for the Nicaraguan Contras and the rightist government of El Salvador in the 1980s. At the time of his retirement in 1993, he was 84th in overall House seniority, dean of the Oregon House delegation, a majority whip-at-large, and a veteran member of the House Appropriations Committee.

AuCoin was a two-term member of the Oregon House of Representatives from 1971 to 1974. In his second term, he was House Majority Leader, at the age of 31. He is a full-time author, writer, lecturer and occasional blogger. AuCoin is a member of the ReFormers Caucus of Issue One. He and his wife Susan live in Portland.

AuCoin was born in Portland, Oregon, on October 21, 1942, to Francis Edgar AuCoin, a short order cook from Portland, Maine, and Alice Audrey Darrar, a waitress from Madras, Oregon. When he was four, his father abandoned the family. Les and his brother Leland moved with their mother to Redmond, Oregon, then a small Central Oregon sawmill and farming town, living on her restaurant wages and tips. AuCoin attended Redmond High School, where he was elected most valuable player on the school's basketball team. He also joined the staff of the school newspaper, where he discovered an aptitude for writing—a skill that would help propel him into journalism, Congress and, in political retirement, life as a writer. In 1960, he became the first male in his extended family to graduate from high school.

AuCoin enrolled at Pacific University in Forest Grove, Oregon, then transferred to Portland State University. In 1961, he enlisted in the United States Army. He was assigned to the 2nd Infantry Division and the 10th Mountain Division where he served as a public information specialist, writing dispatches to The Nashville Banner, the Louisville Courier-Journal, The Nashville Tennessean, Stars and Stripes, and Army Times, among other publications. AuCoin's Army postings included Fort Ord, California; Fort Slocum, New York; Fort Campbell, Kentucky; Fort Benning, Georgia; and Sullivan Barracks, West Germany. While stationed in the segregated South, AuCoin was caught up in a near race riot in reaction to a sit-in by blacks at an all-white lunch counter, an event that crystallized his zeal for progressive politics.

Following his Army career, AuCoin worked for one summer at The Redmond Spokesman newspaper, then returned to Pacific University, where he was hired as the director of the school's public information department and simultaneously completed his Bachelor of Arts degree in journalism in 1969. He married Susan Swearingen in 1964, and the couple had two children: Stacy in 1965 and Kelly in 1967.

In 1968, AuCoin's opposition to the Vietnam War led him to co-chair Eugene McCarthy's Presidential campaign in Oregon's Washington County, west of Portland. AuCoin stayed with McCarthy after President Lyndon B. Johnson dropped out of the race. McCarthy's upset victory over Robert F. Kennedy in the Oregon Democratic primary encouraged AuCoin to run for elective office in 1970, seeking and winning an open seat in the Oregon House of Representatives in Washington County. Two years later, he was re-elected to the 57th Oregon Legislative Assembly. The Democrats took control of the chamber and he was elected House Majority Leader, the second highest position in the House.

During his time in the Oregon House, AuCoin championed environmental, consumer protection, and civil rights issues. As the Democratic floor leader, he helped pass maverick Republican Governor Tom McCall's plan (opposed by legislative Republicans and later rejected by voters) to provide 95% state funding for public schools, enacted statewide land use planning rules, reduced penalties for possession of small amounts of marijuana, and established funding of mass transit from highway funds that had been earmarked solely for roads. AuCoin also chaired the committee that led the efforts to ratify the Equal Rights Amendment.