It's a sad start to the new year for M*A*S*H fans, with news William Christopher is dead at 84.

He was best known for his role in the hit television show, which began in the 70s, where he plays the earnest, soft-spoken US Army priest Father Francis Mulcahy on the hit TV comedy.

Christopher died on Saturday at his home in Pasadena, California. The actor was diagnosed with cancer about 18 months ago, his New York-based agent, Robert Malcolm, told Reuters.

TMZ reports during Christopher's time on Mash, he played a Catholic priest but was a Methodist in real life. When auditioning for the part, he went off script and ad libbed and he was given the job on the condition he wouldn't go off script again.

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Christopher also starred in The Andy Griffith Show, and Hogan's Heroes.

He also made a few appearances on the hit show, The Love Boat.

Christopher was a charitable man and has worked with the National Autistic Society to raise awareness about the organisation. His son Ned was also diagnosed with autism.

Together with his wife, Christopher wrote a book about what it was like to raise a son with autism.

Christopher had small cell carcinoma, a highly malignant cancer that usually arises in the lung.

He died exactly one year after his co-star Wayne Rogers, who died at 82 from complications with pneumonia.