As a radio executive, he helped found Inner City Broadcasting and establish the urban contemporary format, rooted in black music but appealing to a racially diverse audience. In the 1970s, it came to dominate the airwaves, first in New York City — where WBLS became the No. 1 station in the market — and then across the country.

He was the first African-American inducted into the National Association of Broadcasters Hall of Fame, in 1990, and among the first five inducted into the Radio Hall of Fame, in 1995.

“Hal was the constant voice of black America,” the Rev. Al Sharpton said Thursday. “From M.L.K. to a black president, he literally was the one who connected those dots.”

Harold Baron Jackson was born in Charleston, S.C., probably on Nov. 3, 1915. (He explained in his autobiography, “The House That Jack Built,” that his birth, like that of many Southern blacks in those years, was not officially recorded.) He was one of five children of Eugene Baron Jackson, a tailor, and the former Laura Rivers. Both his parents died when he was a child, and he lived with relatives in Charleston and New York before settling in Washington, where he graduated from Dunbar High School and attended classes at Howard University.

Avidly interested in sports, he approached the management of WINX, owned by The Washington Post, in 1939 about covering black sports events for the station. Told that station policy prohibited hiring black announcers, he took a different tack: he persuaded a white-owned advertising agency to buy time on WINX for a 15-minute interview and entertainment show, without revealing that he was involved. As he recalled, he showed up in the studio at the last possible moment and was on the air with “The Bronze Review” before management could stop him.