George Lucas' Ex-Wife and 'Star Wars' Unsung Hero Marcia Lucas Dead at 80

George Lucas's ex-wife Marcia Lucas, an unsung hero of 'Star Wars' who has been called the original film's "secret weapon," is dead ... TMZ has learned.

A rep for the family tells TMZ ... Marcia died on Wednesday from metastatic cancer. We're told she passed peacefully at her home in Rancho Mirage, CA surrounded by loved ones.

Marcia is best known for editing "Star Wars" and "Return of the Jedi" ... earning an Academy Award in 1977 for Best Film Editing for the OG film.

She got her start in editing in the mid-1960s ... securing an apprenticeship during which she edited multiple promotional trailers and commercials.

While working on the documentary "Journey to the Pacific" under Verna Fields -- who would go on to edit "Jaws" -- Marcia met George ... and the two got engaged shortly after.

In 1969, Marcia and George tied the knot.

Their collaborations began in the late 1960s ... Marcia edited George's short film "Filmmaker" and his feature-length directorial debut "THX 1138" before co-editing "American Graffiti" with Fields.

Marcia worked with Martin Scorsese on "Alice Doesn't Live Here Anymore" and "Taxi Driver" ... before jumping into the "Star Wars" editing process after George was horrified by the first rough cut of the movie.

Marcia, Richard Chew, and Paul Hirsch won the Oscar for Best Film Editing at the 50th annual Academy Awards in 1977. Marica later served as an editor of 'Return of the Jedi' ... and she also gave George notes on other projects during their marriage in an unofficial capacity.

Ultimately, in 1983 Marcia and George's marriage came to an end. She married Tom Rodrigues -- a stained glass artist -- later that year, but in 1993 they divorced.

Marcia once expressed regret about the end of her 20 "wonderful years" with George ... telling "Return of the Jedi" actor Michael Pennington she didn't think George had forgiven her for the split.

She was also vocal about the 'Star Wars' universe in recent years ... bashing Kathleen Kennedy and J.J. Abrams for the direction of the sequel series ... saying they just "don't get" the franchise.

Marcia had two daughters -- Amanda Lucas with George and Amy Soper with Tom.

She was 80.