WIKIPEDIA: Marlon Brando became involved with the American Indian Movement (AIM) in the early 1970s. In 1973, he decided to make a statement about the Wounded Knee incident and contacted AIM about providing a person to accept the Oscar for him. Dennis Banks and Russell Means picked Sacheen Littlefeather. She represented Brando and his boycott of the Best Actor Oscar for his portrayal as Don Vito Corleone in The Godfather (1972), as a way to protest the ongoing siege at Wounded Knee and Hollywood‘s and television‘s misrepresentation of American Indians. Brando had written a 15-page speech for Littlefeather to give at the ceremony, but when the producer met her backstage he threatened to physically remove her or have her arrested if she spoke on stage for more than 60 seconds.[5] Her on-stage comments were therefore improvised. She then went backstage and read the entire speech to the press. In his autobiography My Word Is My Bond, Roger Moore (who presented the award and had recently been announced as the new James Bond, Agent 007) claims he took the Oscar home with him and kept it in his possession until it was collected by an armed guard sent by the Academy. The incident provoked the Academy of Motion Picture Arts and Sciences to rule out future proxy acceptance of the Academy Awards.[6] MORE
BUSINESS INSIDER: On March 5, 1973, Marlon Brando declined the Academy Award for Best Actor for his gut-wrenching performance as Vito Corleone in “The Godfather” — for a very unexpected reason. In the 1960s, Brando’s career had slid into decline. His previous two movies — the famously over-budget “One-Eyed Jacks” and “Mutiny on the Bounty” — tanked at the box office. Critics said “Mutiny” marked the end of Hollywood’s golden age, and worse still, rumors of Brando’s unruly behavior on set turned him into one of the least desirable actors to work with.
Brando’s career needed saving. “The Godfather” was his defibrillator. In the epic portrayal of a 1940s New York Mafia family, Brando played the patriarch, the original Don. Though the film follows 
his son Michael (played by Al Pacino), Vito Corleone is its spine. A ruthless, violent criminal, he loves and protects the family by any means necessary. It’s the warmth of his humanity that makes him indestructible — a paradox shaped by Brando’s remarkable performance.
“The Godfather” grossed nearly $135 million nationwide, and is heralded as one of the greatest films of all time. Pinned against pinnacles of the silver screen — Michael Caine, Laurence Olivier, and Peter O’Toole — Brando was favored to win Best Actor. On the eve of the 45th Academy Awards, Brando announced that he would boycott the ceremony and send Sacheen Littlefeather in his place. A little-known actress, she was then-president of the National Native American Affirmative Image Committee.
On the evening of March 5, when Liv Ullman and Roger Moore read out the name of the Best Actor award recipient, neither presenter parted their lips in a smile. Their gaze fell on a woman in Apache dress, whose long, dark hair bobbed against her shoulders as she climbed the stairs. Moore extended the award to Littlefeather, who waved it away with an open palm. She set a letter down on the podium, introduced herself, and said:
“I’m representing Marlon Brando this evening and he has asked me to tell you … that he 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 —”
The crowd booed. Littlefeather looked down and said “excuse me.” Others in the audience began to clap, cheering her on. MORE