Olsen died early Thursday at City of Hope hospital in Duarte while surrounded by his family, his brother Orrin said. He had been diagnosed last year with mesothelioma, a form of cancer that affects the lining of the lungs.
"Merlin Olsen was an extraordinary person, friend and football player," NFL Commissioner Roger Goodell said in a statement. "Merlin was a larger-than-life person, literally and figuratively, and leaves an enormously positive legacy."
Said former Rams teammate Jack Youngblood: "He was compassionate, considerate, articulate, caring. He had all of the intangibles that anyone would want in a husband, a friend, a father. I can't speak highly enough of Merlin Olsen."
With the Rams, Olsen helped popularize the star power of defensive linemen who could sack quarterbacks. The Fearsome Foursome of Olsen, David "Deacon" Jones, Roosevelt "Rosey" Grier and Lamar Lundy, standout talents on mediocre teams from 1963 to 1966, used size, speed and skill to terrorize offenses.
"Our philosophy was that they can't double-team all of us," Olsen said in a 1985 interview with The Times. "Somebody would be one-on-one and he'll get the quarterback. There were times, though, when teams would double-team all four of us or change their blocking patterns just to hold us down -- which was a nice compliment."
At 6 feet 5 and 275 pounds, Olsen was a dominating physical presence at left tackle, but he also was known for his analytical approach to the game.
"I was amazed by his size just like everybody else, but more than that at his great intelligence," former CBS analyst Irv Cross, who played three years with Olsen on the Rams, told The Times in 1982. "His ability to analyze the game was something everybody on the team recognized. It was just unbelievable that any one person would be gifted in so many ways."
Merlin Jay Olsen was born Sept. 15, 1940, in Logan, Utah, the second of nine children of Lynn Jay and Merle Olsen.
He was a three-time academic All-American at Utah State, where in 1962 he won the Outland Trophy as the nation's best interior lineman.
He graduated summa cum laude with a bachelor's degree in finance in 1962 and later studied during the NFL off-season to earn a master's in economics from Utah State in 1970.
Olsen was the third player picked in the 1962 NFL draft, right after his longtime Rams teammate, quarterback Roman Gabriel. Olsen immediately became a starter, but the team was dreadful, winning only one game in his rookie season.
The Rams didn't begin winning consistently again until the late 1960s, and in 1968 the defense set an NFL record for yielding the fewest yards in a 14-game season.
Despite being on some good teams during the later part of his career, Olsen never made it to the Super Bowl as a player.
"That's one goal I didn't reach. But as a professional athlete, I reached or surpassed most every other [goal] a number of times," he told the Salt Lake Tribune in 1994.
Olsen, who remains the Rams' all-time leader in career tackles with 915, was elected to the Pro Football Hall of Fame in 1982, his first year of eligibility.
He quickly adjusted to life after football and was best known at NBC for his pairing with Dick Enberg, who used to call the Rams' games on radio.
"He was so thoroughly prepared, he should have been a lawyer," Enberg told The Times in 2006. "He was so competitive in all the good ways. . . . We all have the perfectionist complex, but he carried it out in the most noble and social way because he didn't jump on anybody or walk on anybody to get to where he was. He did it all the right ways."