William L. Clay, who became the first African-American elected to the House of Representatives from Missouri, co-founded the Congressional Black Caucus and forcefully promoted the interests of poor people in St. Louis and beyond in his 32 years on Capitol Hill, died on Thursday in Adelphi, Md. He was 94.

His son, William L. Clay Jr., who was elected in 2000 to take his father’s House seat and served until 2021, confirmed the death, at the home of Mr. Clay’s daughter Vicki Jackson. He lived in Silver Spring, Md.

From his election in 1968 until he retired after 16 terms rather than run again in 2000, Mr. Clay had no interest in legislating or lobbying for those who enjoyed prosperity and influence. “I don’t represent all people,” he said in an interview with The New York Times during his 1982 campaign. “I represent those who are in need of representation. I have no intention of representing those powerful interests who walk over powerless people.”

An uncompromising liberal Democrat, Mr. Clay was one of 13 founders of the Congressional Black Caucus, organized in early 1971 to concentrate on issues directly affecting Black Americans. At once, he moved to set the caucus on an aggressive course as it boycotted President Richard M. Nixon’s State of the Union address in January 1971.

“We now refuse to be part of your audience,” Mr. Clay wrote to Nixon on behalf of the caucus, whose members were unhappy with the president’s initial reluctance to meet with the group. When Nixon did meet with the caucus that March, each member cited a major concern for Black constituents. Mr. Clay said federal grants were needed to help impoverished Black students repay loans for their education.