Adlai Stevenson III, a former senator from Illinois who was descended from a prominent political family, died Sept. 6 at his home in Chicago. He was 90.

       His son Adlai Stevenson IV told the Chicago Sun-Times his father had dementia.

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       Mr. Stevenson was the great-grandson of former vice president Adlai Stevenson. His father, Adlai Stevenson II, was a former Illinois governor and two-time Democratic presidential candidate who lost to Dwight D. Eisenhower in 1952 and 1956.

       After the death in 1969 of longtime Illinois Sen. Everett M. Dirksen (R), another Republican, Ralph Tyler Smith, was appointed to the seat.

       Mr. Stevenson, who had served in the Illinois legislature and as state treasurer, contemplated a run for the Senate and sought the advice of then-Chicago Mayor Richard J. Daley.

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       “My advice to you is don’t change your name,” Daley reportedly told him.

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       Mr. Stevenson handily defeated Smith in a 1970 special election to complete the remaining four years of Dirksen’s term.

       In the Senate, Mr. Stevenson sponsored a bill calling for the end of U.S. aid to Vietnam by 1975. He was also the first chairman of the Senate Ethics Committee and helped draft a code of ethics for the Senate. He also served on the Commerce, Banking and Intelligence committees.

       He was reelected with 62 percent of the vote in 1974 but chose not run again in 1980.

       Mr. Stevenson ran for governor of Illinois twice, losing in 1982 to incumbent Republican Gov. James R. Thompson by 5,074 votes out of more than 3.6 million votes cast. The results were disputed, but the state Supreme Court declined to order a recount.

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       In 1986, Mr. Stevenson won the Democratic nomination for governor but ran as a candidate of the newly formed Illinois Solidarity Party, losing again to Thompson.

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       Adlai Ewing Stevenson III was born Oct. 10, 1930, in Chicago. He graduated from the private Milton Academy in 1948 and from Harvard College in 1952. He served in the Marine Corps in the Korean War and in 1957 graduated from Harvard Law School.

       He practiced law in Chicago before entering politics. After leaving the Senate, Mr. Stevenson worked on international finance issues, particularly in Asia, and managed a family farm near Galena, Ill.

       Survivors include his wife of 66 years, the former Nancy Anderson; four children; two brothers; and nine grandchildren.

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