'Survivor' Contestant Roger Sexton Dead at 76

"Survivor" contestant Roger Sexton has passed away ... after fighting a lengthy battle with dementia.

Family members confirmed that Roger passed away at his daughter and son-in-law's home at the end of October, surrounded by family and caretakers in Walla Walla, Washington.

His obituary states his death follows "a valiant and courageous battle with Lewy Body Dementia" -- the 2nd most common form of the disease, following Alzheimer's.

Fans of the show remember Roger from the 6th season of the reality competition series -- he was on the Tambaqui tribe, and became a leader for his team fairly quickly.

Roger lasted a total of 21 days out in the Amazon ... eventually getting blindsided by the opposing tribe, which got several members of his own team to turn against him.

Roger was a retired Marine -- he served in the Vietnam war in the '60s. He tragically lost his daughter Heather in 1992 when she died of viral pneumonia.

Roger was 76.