Merlin Olsen, the Hall of Fame tackle who anchored the Los Angeles Rams’ Fearsome Foursome, the line that glamorized defensive play in the National Football League, died early Thursday at a hospital in Duarte, Calif. He was 69.

His death was announced by his brother Orrin, who said he had been treated for mesothelioma, a rare form of cancer involving a membrane that covers and protects most of the body’s internal organs. Until his hospitalization he had lived in Park City, Utah.

Olsen was considered one of the greatest tackles in N.F.L. history, but he also forged careers in broadcasting and acting. He was a longtime color commentator for NBC’s pro football and Rose Bowl telecasts, working with Dick Enberg, and he acted on television, most prominently in NBC’s “Little House on the Prairie” and in his own series, “Father Murphy.”

In the early 1950s, the Rams boasted a high-powered offense, led by quarterbacks Norm Van Brocklin and Bob Waterfield and receivers Tom Fears and Crazy Legs Hirsch. The Rams of the mid-1960s were renowned for defensive linemen who earned a collective nickname a decade before the Pittsburgh Steelers’ Steel Curtain.

The Rams had only one winning season from 1963 to 1966, the span in which all four Fearsome players were teammates, but those linemen were celebrated for their strength, flair, know-how and agility.

Olsen, 6 feet 5 inches and 270 pounds or so, played left tackle, jamming up the middle, stopping draw plays and screen passes and often pressuring the quarterback. Deacon Jones, another eventual Hall of Famer, extremely quick and adept at the head slap, lined up at left end. Jones joined with Lamar Lundy, the right end, in rolling up the sacks while Roosevelt Grier, the former Giants star, was a formidable presence at right tackle.

“Merlin had superhuman strength,” Jones told The Los Angeles Times in 1985. “If I was beating my man inside, he’d hold him up and free me to make the tackle. If he had to make an adjustment to sacrifice his life and limb, he would make it. A lot of the plays I made were because he or the others would make the sacrifice.”

Olsen felt that the Fearsome Foursome could have excelled in any era.

“What made the Foursome unique, I think, is that we could have fit in extremely comfortably in the modern game,” he told The Orange County Register in 1997. He estimated that the line’s average weight was 275 pounds and said that “there was not a weight lifter in the group.”

“Imagine how big we’d be today,” he added.

“We could all run,” Olsen said. “The other thing we had going for us was a rare chemistry. There was also a very special kind of unselfishness.”

Joining the Rams in 1962 from Utah State University, where he won the Outland Trophy as college football’s best interior lineman, Olsen spent his entire 15-year career with Los Angeles.

Olsen was voted to the Pro Bowl every year except for his final season, he was an all-N.F.L. selection six times, and he was chosen by the Maxwell Club of Philadelphia as the N.F.L.’s most valuable player in 1974. He was voted into the College Football Hall of Fame in 1980 and the Pro Football Hall of Fame in 1982. He was named, along with Jones, to the 75th anniversary all-N.F.L. team in 1994 in a vote by the news media and league personnel.

Olsen may have exuded a fearsome presence in his own right, but he was hardly a brute. He was named one of the nation’s top scholar athletes by the National Football Foundation in his senior year at Utah State and he received a master’s degree in economics while playing for the Rams.

Merlin Jay Olsen, a native of Logan, Utah, was born on Sept. 15, 1940. He was so awkward while pursuing sports in the ninth grade that a coach discouraged him from athletic aspirations.

“I was either stubborn or foolish, but I was unwilling to give up on my dreams,” The South Bend Tribune quoted him as telling a College Football Hall of Fame luncheon in 2007.

Olsen played a major role in reviving the football program at Utah State, leading the Aggies to appearances in the Sun Bowl and the Gotham Bowl. He was one of the Rams’ two first-round draft picks in 1962, going third over all after they drafted quarterback Roman Gabriel.

Olsen was the N.F.L.’s rookie of the year on a team that won only one game. The Rams began a turnaround in 1966, when George Allen became the head coach, but Olsen never reached the Super Bowl.

In February 1977, shortly after retiring, Olsen signed a contract with NBC. In addition to working alongside Enberg in the broadcast booth, he appeared for several seasons with Michael Landon in “Little House on the Prairie” as the very large and bearded lumberman Jonathan Garvey.

From 1981 to 1983 he had the title role in NBC’s “Father Murphy,” in which he played an 1870s frontiersman who disguises himself as a priest to shelter orphans. In the short-lived “Fathers and Sons” he played a baseball coach, and in “Aaron’s Way,” a 1988 series, he was the head of an Amish family that leaves its traditional lifestyle behind and moves to California.

“I was raised in a very strict Mormon home and in a Mormon community,” The Post-Standard of Syracuse quoted him as saying when he took the role of the Amish patriarch Aaron Miller. “There are certain things I can lean back on and remember in a family situation that helped me to work as an actor.”

Olsen also had roles in television movies, made numerous guest appearances in a variety of TV series and was a familiar figure in commercials as a spokesman for FTD florists.

Utah State brought an ailing Olsen back to the campus for a halftime ceremony of a basketball game in December 2009, when the university announced it would dedicate the football field at its Romney Stadium as Merlin Olsen Field in 2010. The St. Louis Rams — the Los Angeles Rams’ successor franchise — honored Olsen at a home game that month, although he was unable to attend because of his illness.

Olsen was one of three brothers who played in the N.F.L. Phil Olsen was a teammate, playing defensive tackle for the Rams from 1971 to 1974 and later playing for the Denver Broncos. Orrin Olsen played center for the Kansas City Chiefs.

In addition to Phil and Orrin, Olsen is survived by his wife, Susan; their children Nathan, Jill and Kelly; his brother Clark; his sisters Colleen, Lorraine, Gwen, Winona and Ramona; and several grandchildren.

Olsen overpowered many an offensive lineman, but he had something of a mild-mannered outlook.

“I’m sure that I take out many of my personal aggressions on the field, but I don’t play football for that reason,” he remarked in the N.F.L.’s “The First 50 Years: The Story of the National Football League.”

“My roughness and aggressiveness at certain times are prompted by my desire to be a better football player. I don’t enjoy contact.”