Bottoms died Tuesday at his home in Los Angeles of glioblastoma multiforme, a virulent brain cancer, said his wife, Laura Bickford. The brother of actors Timothy, Joseph and Ben Bottoms, Sam made his screen debut as a teenager inPeter Bogdanovich's 1971 film "The Last Picture Show," in which Timothy played one of the leads. Sam played Billy, the mute, mentally handicapped boy.
Then 15, he hadn't expected to be cast in the movie.
Bottoms had traveled from his home in Santa Barbara to Archer City, Tex., to observe the filming, he recalled in a 1993 interview with the Houston Chronicle.
He was sitting on a street corner drinking a Dr. Pepper with his brother when a station wagon rolled by and stopped.
"Peter Bogdanovich gets out," Bottoms recalled, "and says, 'What's your name?' "
When he said he had come to visit his brother, Bogdanovich surprised him by asking, "Do you want to be in the movie?"
Since then, Bottoms appeared in some 30 films, including Clint Eastwood's "The Outlaw Josey Wales" and "Bronco Billy." More recently, he appeared in "SherryBaby," "Shopgirl" and "Seabiscuit."
He also made guest appearances on TV series such as "NYPD Blue," "The X Files," "Murder, She Wrote" and "21 Jump Street." And he played Cal Trask in the 1981 TV mini-series "East of Eden."
Bottoms was 20 in 1976 when he was cast to play surfer Lance Johnson in "Apocalypse Now," in which he was one of the young sailors who accompany Capt. Benjamin Willard (Martin Sheen) up river in a gunboat for his rendezvous with Marlon Brando's renegade Col. Walter Kurtz.
That comes after Bottoms' scenes with Robert Duvall's surf-obsessed Lt. Col. Bill Kilgore, who memorably calls in a napalm strike on the tree line behind a coastal village with a primo surf spot.
Bottoms spent a year and a half filming the movie in the Philippines.
"Francis is a great general, he's a Gen. Patton, a Gen. Sherman, a great leader," Bottoms said in a 2001 interview with The Times. "I was his loyal soldier. I would have done anything he asked. I did, and I'm surprised that I came out of it alive."
Coppola told The Times on Wednesday that in casting young actors to play soldiers in the movie, he had been impressed with Bottoms during improvisational sessions.
"He was a handsome, tall young man and very sweet-natured and seemed to be right for that part," Coppola said. "He, Larry Fishburne and Fred Forrest were like a young family almost to me [during filming], and they went through thick and thin uncomplainingly. We all admired them.
"Sam was an especially likable, beautiful young man. He was quiet and undemanding and always anxious to help and had a nice smile."
Bottoms later played a lieutenant in Coppola's "Gardens of Stone," a 1987 military film set during the Vietnam era.
"Sam was a good actor. Of course, he comes from a family that had a lot of theatrical activity," Coppola said.
Bottoms was born in Santa Barbara on Oct. 17, 1955, and began acting in the Santa Barbara Youth Theatre at age 10.
In addition to his wife, he is survived by his two daughters from his first marriage to Susan Arnold, Io and Clara Bottoms; his three brothers; his father, James "Bud" Bottoms; and his mother, Betty Bottoms.
A private funeral will be held today, and a memorial service will be held sometime early next year.
Instead of flowers, donations may be made to Angels Among Us at the Preston Robert Tisch Brain Tumor Center at Duke University, DUMC Box 3624, Durham, N.C., 27710 .