Native American actress and activist Sacheen Littlefeather who came to the Academy's agenda when they apologized after 50 years for the abuse she was subjected to when she took the stage to decline the award on behalf of Marlon Brando and spoke up for Indigenous rights in 1973, died on Sunday at the age of 75.

The Academy announced her death in a tweet that quoted Littlefeather as saying: "When I am gone, always be reminded that whenever you stand for your truth, you will be keeping my voice and the voices of our nations and our people alive."

Two weeks ago, the Academy held a ceremony at its new Los Angeles museum honoring Littlefeather and publicly apologizing for her treatment at the Oscars ceremony.

Littlefeather, who is of Apache and Yaqui heritage, was booed at the 1973 Academy Awards - the first to be broadcast live around the world - while explaining on Brando's behalf why he would not accept his Best Actor Oscar for "The Godfather."

Brando had asked Littlefeather to decline the award for him in an act of protest against the treatment of Native Americans by the film industry. "I went up there, like a proud Indian woman with dignity, with courage, with grace, and with humility," Littlefeather said at the museum event.

"I knew that I had to speak the truth. Some people may accept it. And some people may not."

She said Western star John Wayne had to be restrained from physically assaulting her as she left the stage.

Littlefeather, a member of the Screen Actors' Guild, subsequently found it difficult to get work in Hollywood, with casting directors warned not to employ her.

Asked by reporters ahead of the ceremony how she felt about having to wait so long to hear the word "sorry," Littlefeather was philosophical. "It's never too late for an apology," she said.

"It's never too late for forgiveness."