David Ross Obey (/ˈoʊbiː/ OH-bee; born October 3, 1938) is an American lobbyist and former politician who served as a member of the United States House of Representatives for Wisconsin's 7th congressional district from 1969 to 2011. The district includes much of the northwestern portion of the state, including Wausau and Superior. He is a member of the Democratic Party, and served as Chairman of the powerful House Committee on Appropriations from 1994 to 1995 and again from 2007 to 2011. Until he was surpassed by Jim Sensenbrenner in 2020, Obey was the longest-serving member ever of the United States House of Representatives from the state of Wisconsin. Obey remains the longest serving Democratic Representative from Wisconsin.

Obey was born in Okmulgee, Oklahoma, the son of Mary Jane (née Chellis) and Orville John Obey. In 1941, his family moved back to his parents' native Wisconsin, and Obey was raised in Wausau, Wisconsin, where he has lived since. He graduated from Wausau East High School and initially attended the University of Wisconsin branch campus at Wausau to save money before transferring to the University of Wisconsin–Madison, where he received his Bachelor of Arts degree in political science from and did graduate work in Soviet politics at the University of Wisconsin under a National Defense Education Act three-year scholarship.

During his youth, Obey identified as a Republican, and helped deliver campaign material for Joseph McCarthy during his electoral campaigns. However, he left the party after seeing one of his teachers falsely branded as a communist by supporters of Senator Joseph McCarthy. Obey also had come to identify with the progressive philosophy of Robert M. La Follette and began working for the electoral campaigns of Democrats such as Gaylord Nelson, Robert Kastenmeier, and William Proxmire, becoming affiliated with the Democratic Party sometime in the mid-1950s during his teenage years.

Before serving in Congress, Obey worked as a real estate broker.

He was elected to the Wisconsin State Assembly in 1963 and served there until 1969. During his time in the state legislature he rose to the position of Assistant Majority leader for the Democratic caucus. Obey served in that role from 1967 until 1969, when he left the legislature to serve in the U.S. House of Representatives.

Obey was elected to the House to replace eight-term incumbent Republican Melvin R. Laird, who was appointed Secretary of Defense under President Richard Nixon. Obey, only 30 when he was elected, became the youngest member of Congress upon taking his seat, as well as the first Democrat to represent the district in the 20th century. He was elected to a full term in 1970 and was reelected 18 times. Obey faced his closest race in 1972, during his bid for a second full term, when his district was merged with the neighboring 10th District of Republican Alvin O'Konski, a 15-term incumbent. However, Obey retained 60 percent of his former territory, and was handily reelected in subsequent contests.

In Congress, Obey chaired the commission to write the House's Code of Ethics. Among the reforms he instituted was one requiring members of the House to disclose their personal financial dealings so the public would be made aware of any potential conflicts of interest. Obey served as chairman of the House Appropriations Committee from 2007 to 2011; he briefly chaired this committee from 1994 to 1995 and served as its ranking Democrat from 1995 to 2007. He also chaired its Subcommittee on Labor.

Obey was one of the most liberal members of the House; he considers himself a progressive in the tradition of Robert La Follette. Obey had risen to the position of fifth ranking House Democrat since his party retook control of Congress.