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 voracious gentile girlfriend, known as the Monkey. In “The Great Gatsby” (1974), the generally dismissed version of Fitzgerald’s novel that starred Robert Redford, she was Myrtle Wilson, the crass, pathetic and doomed paramour of Tom Buchanan (Bruce Dern).

In “Nashville” (1975), Robert Altman’s witty riff on celebrity, politics and country music, she played Connie White, a veteran singer with a cynical competitive edge, a role for which she wrote and performed her own songs. And in “The Day of the Locust” (1975), John Schlesinger’s adaptation of Nathanael West’s Hollywood-as-hell novel, she was a central character, Faye Greener, a tough, slatternly, aspiring star.

“Black brings to all her roles a freewheeling combination of raunch and winsomeness,” Time magazine wrote about her in 1975. “Sometimes she is kittenish. At other times she has an overripe quality that makes her look like the kind of woman who gets her name tattooed on sailors.”

Her other credits in that period included the disaster film “Airport 1975” (1974), in which she was a stewardess who took over the controls of a disabled plane; “Family Plot” (1976), Alfred Hitchcock’s final film, a wickedly comic murder mystery, in which she played a kidnapper; and, somewhat anomalously, “Rhinoceros” (1974), the screen adaptation of Ionesco’s absurdist play.

Ms. Black was nominated for an Academy Award as best supporting actress for her performance in “Five Easy Pieces” as a tenderhearted woman who was out of her intellectual league with her boyfriend, a gifted but angry and restless pianist, and his highbrow family.

That film was released in 1970, just a year after her brief but provocative turn in “Easy Rider” as a companionable hooker who swings between agony and ecstasy after she’s fed a tab of acid by Mr. Fonda in a New Orleans cemetery during Mardi Gras. Together, the films made her something of an “it” girl, a favorite of critics and reporters determined to identify the character of an elusive free spirit.

“She could be a Mount Holyoke senior intent on saving the whooping crane,” Tom Burke wrote in The New York Times in 1970, describing his first impression of her at her home in Hollywood. “What she really is, of course, is a splendid actress who literally turned herself into the tough, acid-tripping New Orleans whore of ‘Easy Rider,’ and then became Rayette Dipesto, the loving, mediocre and totally unforgettable waitress of ‘Five Easy Pieces,’ and if she is not those characters, not super-hip, neither is she just what she appears to be, waiting on this sunny terrace like a ripening apple. Oh, she is warm, accessible; she is also shrewd, worldly, changeable, a subtle comic, and something of a freak, a beautiful freak.”

Karen Blanche Ziegler was born in Park Ridge, Ill., on July 1, 1939, to Norman Ziegler and the former Elsie Reif, the author of a few novels.

She studied drama for two years at Northwestern University before decamping for New York City, where she appeared in a pair of Off Broadway revues — she composed the music for one of them — and took classes with Lee Strasberg, though the two did not get along.

She was hired for the role of Philia, the virgin courtesan (and the ingénue lead), in the Stephen Sondheim musical “A Funny Thing Happened on the Way to the Forum,” but was replaced (by Preshy Marker) during a pre-Broadway tryout. She did land on Broadway in a 1965 thriller, “The Playroom,” starring as a youthful kidnapper, and in 1967 she appeared in Francis Ford Coppola’s early film “You’re a Big Boy Now.”

By the time the 1970s turned to the ’80s, her career had taken a sideways turn. She never stopped working — her list of credits, largely in independent films, is extensive — but her roles in ambitious, groundbreaking films were largely behind her.

Her best-known later title was “Come Back to the 5 & Dime, Jimmy Dean, Jimmy Dean,” about the reunion of a James Dean fan club in a small Texas town 20 years after his death. Directed by Mr. Altman, it was perhaps his most grievous misfire; he had also directed the stage play, by Ed Graczyk, on Broadway, and both were roundly panned. The film and the play starred Sandy Dennis, Cher and Ms. Black, who played a transsexual.

Otherwise, after starring in a 1975 television movie, “Trilogy of Terror,” in which she played the lead role in three different tales of creepiness, she seemed to specialize in horror movies and thrillers, appearing in films like the 1986 remake of “Invaders From Mars” and Rob Zombie’s “House of 1,000 Corpses.” On television, she made guest appearances on series including “In the Heat of the Night,” “Profiler,” “Party of Five” and “Law & Order: Criminal Intent.”

Ms. Black was married and divorced three times before marrying Mr. Eckelberry in 1987. In addition to him, survivors include a son, Hunter Carson; two daughters, Celine Eckelberry and Diane Koehnemann Bay; a sister, Gail Dugan; a brother, Peter Ziegler; four grandchildren; and two great-grandchildren.

Over the years Ms. Black became known for candid, if sometimes loopy, responses to interviewers’ questions.

“Rafelson thought I might be too complex for Rayette, but I told him I’m essentially simple, that really everybody is essentially simple, that we are all just beings who, uh, be,” Ms. Black said in 1970, referring to Bob Rafelson, the director of “Five Easy Pieces,” and her character.

“Certainly Rayette can just be,” she said. “I dig her, she’s not dumb, she’s just not into thinking. I didn’t have to know anybody like her to play her. I mean, I’m like her, in ways. Rayette enjoys things as she sees them, she doesn’t have to add significances. She can justlove the dog, love the cat. See? There are many things she does not know, but that’s cool; she doesn’t intrude on anybody else’s trip. And she’s going to survive. Do you understand me?”