He had a firebrand’s face: wreathed in a gray beard and a shock of unruly hair, with dark, uncompromising eyes. Once, a student asked what made him tick. “Rage,” he replied. But he said it softly, and friends recalled that his invective, in print or in person, usually came wrapped in gentle good humor and respectful tones.

Nathan Irving Hentoff was born in Boston on June 10, 1925, the son of Simon and Lena Katzenberg Hentoff. His parents were Jewish immigrants from Russia, and he grew up in the tough Roxbury section in a vortex of political debate among Socialists, anarchists, Communists, Trotskyites and other revolutionaries. He learned early how to rebel.

In 1937, on Yom Kippur, the Jewish day of atonement and fasting, the 12-year-old Nat sat on his porch on a street leading to a synagogue and slowly ate a salami sandwich. It made him sick, and the action outraged his father. He had not done it to scandalize passing Jews who glared at him, he said in a memoir, “Boston Boy” (1986). “I wanted to know how it felt to be an outcast,” he wrote. “Except for my father’s reaction and for getting sick, it turned out to be quite enjoyable.”

He attended Boston Latin, the oldest public school in America, and read voraciously. He discovered Artie Shaw and fell passionately for Louis Armstrong, Bessie Smith, Duke Ellington, Fats Waller and other jazz legends. As more modern styles of jazz emerged, Mr. Hentoff also embraced musicians like Thelonious Monk, Charlie Parker, Charles Mingus and, later, Ornette Coleman and Cecil Taylor.

At Northeastern University, he became editor of a student newspaper and turned it into a muckraker. When it dug up a story about trustees backing anti-Semitic publications, the university shut it down. Mr. Hentoff and members of his staff resigned, but he graduated in 1946 with high honors and a lasting devotion to the First Amendment.

After several years with a Boston radio station, he moved to New York in 1953 and covered jazz for Down Beat until 1957.