Ed Sadlowski, a fireball labor leader whose militant insurgency in the 1970s shook but failed to dislodge the steelworkers union’s top brass, died on Sunday in Estero, Fla. He was 79.

His death was confirmed by his daughter Susan Sadlowski Garza, a Chicago alderwoman. He had Lewy body dementia, she said.

Mr. Sadlowski, a third-generation steelworker who dropped out of high school in the 11th grade to become an apprentice machinist, rose meteorically through the ranks of the United Steelworkers union by echoing the confrontational rhetoric of his labor heroes, like John L. Lewis, who had led the miners union, and Victor Reuther, one of three Reuther brothers who had transformed the autoworkers union into a labor power.

Mr. Sadlowski rejected the more collegial approach of contemporaries who had gone so far as to give up the right to strike in favor of arbitration.