Edward Brooke, the first black senator to be popularly elected in the US, has died aged 95, Republican Party officials say.
Mr Brooke was elected to Congress in 1966 by voters in Massachusetts at a time of widespread racial unrest.
A former lawyer, he had also been the first African-American to hold the post of attorney general in any state when he was elected senator.
Two black senators before him were both picked by state legislatures.
President Barack Obama said in a statement: “Senator Brooke led an extraordinary life of public service.
“Ed Brooke stood at the forefront of the battle for civil rights and economic fairness.”
Massachusetts Governor Deval Patrick said: “I have lost a friend and mentor.”
Senate Republican leader Mitch McConnell said: “Senator Brooke’s accomplishments remind us that anything is possible in our country.”
Breast cancer awareness
Mr Brooke served in the Senate until 1979 and is one of only nine African-Americans to do so, including President Obama.
Mr Brooke built a reputation as a Republican liberal during his time in the Senate. He opposed Republican President Richard Nixon and was the first Republican senator to publicly call for Mr Nixon’s resignation after the Watergate scandal.
He was instrumental in passing the Fair Housing Act of 1968, which prohibited racial and religious discrimination.
Mr Brooke was re-elected in 1972 by a huge margin but by the time he ran for a third term, he was involved in a divorce which attracted national attention and raised questions about a false financial statement he had made regarding a $49,000 loan.
He lost his bid for the third term in 1978 and returned to private law practice.
In 2002, Mr Brooke was diagnosed with breast cancer and became a national leader in raising awareness of the disease in men, which occurs much less frequently than in women.