NFL commissioner Roger Goodell issued a statement lauding Olsen as an "extraordinary person, friend and football player."
"He cared deeply about people, especially those that shared the game of football with him," Goodell said. "Merlin was a larger-than-life person, literally and figuratively, and leaves an enormously positive legacy."
Olsen was an All-American at Utah State and a first-round draft pick of the Los Angles Rams in 1962.
The giant from northern Utah joined Deacon Jones, Lamar Lundy and Rosey Grier on the Rams' storied "Fearsome Foursome" defensive line known for either stopping or knocking backward whatever offenses it faced. The Rams set an NFL record for the fewest yards allowed during a 14-game season in 1968.
Olsen was rookie of the year for the Rams in 1962 and is still the Rams' all-time leader in career tackles with 915. He was named to 14 consecutive Pro Bowls, a string that started his rookie year.
Olsen was also an established television actor with a role on "Little House on the Prairie," then starring in his own series, "Father Murphy," from 1981 to 1983 and the short-lived "Aaron's Way" in 1988.
Olsen was a consensus All-American at Utah State and won the 1961 Outland Trophy as the nation's best interior lineman. The Rams drafted Olsen third overall in 1962 and he spent the next 15 years with the team before retiring in 1976.
Utah State honored Olsen in December by naming the football field at Romney Stadium "Merlin Olsen Field." Because of his illness, Olsen's alma mater didn't want to wait until football season and made the announcement during halftime of a basketball game.
Olsen was well enough to attend, but did not speak at the event. He stood and smiled as he waved to fans during a standing ovation and chants of "Merlin Olsen!" and "Aggie Legend!"
Utah State is also planning a statue of Olsen at the southeast corner of the stadium.
"This was the voice of a man who not only became one of our country's most decorated athletes, but also one of the most accomplished and respected people ever to hail from the state of Utah," said Stan Albrecht, president of Utah State.
The Rams also honored Olsen during a game Dec. 20, with a video tribute narrated by Dick Enberg, Olsen's longtime broadcast partner. Olsen did not attend because of his health. His name was already part of the Ring of Fame inside the Edward Jones Dome in St. Louis along with other franchise standouts.
He was voted NFC defensive lineman of the year in 1973 and the NFL MVP in 1974, and was voted to the Pro Football Hall of Fame in 1982.