Sacheen Littlefeather, the Native American activist who declined Marlon Brando's Best Actor Oscar for him in a memorable 1973 speech, passed away on Sunday. She was 75 years old.

Littlefeather died at her home in Novato, California, after a years-long battle with breast cancer, which eventually metastasized to her right lung. The activist, who also worked as an actress, changed her name from Marie Louise Cruz to Sacheen Littlefeather after rediscovering her Native American heritage and becoming active in protests as a young woman.

After Liv Ullmann and Roger Moore announced that Marlon Brando won Best Actor for his performance as Vito Corleone in "The Godfather", Littlefeather surprised audiences by walking on stage in his place.

In a speech that shocked the country at the time, the 26-year-old Apache activist began by introducing herself and explaining that she was representing the "Godfather" actor.

ACADEMY APOLOGIZES TO SACHEEN LITTLEFEATHER NEARLY 50 YEARS AFTER REJECTING AN OSCAR ON MARLON BRANDO'S BEHALF

Sacheen Littlefeather declining Oscar award

At the 1973 Academy Awards, Sacheen Littlefeather refused the Academy Award for Best Actor on behalf of Marlon Brando who won for his role in The Godfather. (Bettmann via Getty Images)

"[Brando] very regretfully cannot accept this very generous award. And the reasons for this being are the treatment of American Indians today by the film industry – excuse me – and on television in movie reruns, and also with recent happenings at Wounded Knee," she said, referencing the Wounded Knee Occupation of 1973.

"I beg at this time that I have not intruded upon this evening, and that we will in the future, our hearts and our understandings, will meet with love and generosity," she added.

Littlefeather, who appeared nervous during her speech and was booed by a few attendees, received both harassment and praise after the event. In August, the Academy wrote a formal apology to her for the "emotional burden" that she carried for 49 years.

Sacheen Littlefeather holding Brando's statement

Sacheen Littlefeather holds a written statement from actor Marlon Brando refusing his Best Actor Oscar on stage at the Academy Awards, Los Angeles, California. (Hulton Archive/Getty Images)

"The abuse you endured because of this statement was unwarranted and unjustified," David Rubin, president of the Academy of Motion Picture Arts and Sciences, wrote to Littefeather. "The emotional burden you have lived through and the cost to your own career in our industry are irreparable."

CLICK HERE TO SIGN UP FOR THE ENTERTAINMENT NEWSLETTER

"For too long the courage you showed has been unacknowledged. For this, we offer both our deepest apologies and our sincere admiration," he added.

Two weeks before her death, the Academy honored her at an event called "An Evening with Sacheen Littlefeather." On Sunday, the Academy tweeted a quote the activist made about her legacy.

Sacheen Littlefeather smiling

Sacheen Littlefeather on stage at AMPAS Presents An Evening with Sacheen Littlefeather at Academy Museum of Motion Pictures on September 17, 2022, in Los Angeles, California. (Frazer Harrison/Getty Images)

"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," the quote read.

CLICK HERE TO GET THE FOX NEWS APP

Littlefeather's family asked mourners to make donations to American Indian Child Resource Center in Oakland, California.