Karen Black, an actress whose roles in several signature films of the late 1960s and ’70s included a prostitute who shared an LSD trip with the bikers played by Dennis Hopper and Peter Fonda in “Easy Rider” and a waitress unhappily devoted to the alienated musician played by Jack Nicholson in “Five Easy Pieces,” died on Thursday in Los Angeles. She was 74.
The cause was complications of cancer, her husband, Stephen Eckelberry, said. Ms. Black’s battle with ampullary cancer, a rare form similar to pancreatic cancer, became public in March when she and Mr. Eckelberry sought contributions on a fund-raising Web site to pay for an experimental treatment.

Ms. Black began her career as a stage ingénue but was never really the ingénue on the screen. A rangy, imperfect beauty — her eyes were set ever so slightly off-kilter — she spent the better part of a decade as one of the movies’ most vivid character actresses. At a time when the women’s movement was surging, she rarely played the self-liberating woman — as did, say, Ellen Burstyn or Jill Clayburgh — but she was often a brassy, attention-grabbing presence in films whose main characters were men.

In “Drive, He Said” (1971), Mr. Nicholson’s directorial debut, she played a faculty wife in an affair with a college athlete (William Tepper). In “Portnoy’s Complaint” (1972), based on Philip Roth’s dark comedy about the libidinous life a young Jewish lawyer (Richard Benjamin), she played his sexually v.