Nielson died of complications from pneumonia at a hospital near his home, surrounded by his wife, Barbaree, and friends, his agent, John S. Kelly, said in a statement.
"Airplane!," the 1980 send-up of just about every disaster movie plot imaginable, Nielsen as Dr. Rumack was "an essentially serious actor taking essentially preposterous material very straight," wrote Times Arts Editor Charles Champlin in his review.
Just how preposterous was it?
As the crew and passengers became ill, Nielsen said they needed to get the sick to a hospital.
"A hospital? What is it?" a flight attendant asked.
Nielsen: "It's a big building with patients, but that's not important right now."
And when Nielsen was told, "Surely you can't be serious," he answered: "I am serious, and don't call me Shirley."
Nielsen followed up "Airplane!" with another goofy role delivered with deadpan conviction as Frank Drebin in the "Police Squad!" television show and "Naked Gun" movies.
It was quite a career shift for an actor who seemed perfectly cast as a handsome leading man when he came to Hollywood in the 1950s, already a veteran of live television appearances.
A typically serious early role was as the spaceship commander in "Forbidden Planet, " the 1956 science-fiction classic. "It's the reason I was never asked to do 'Star Trek' or 'Twilight Zone' for TV," he told the Toronto Star in 2002. "I carried too much baggage with me from that movie."
Nielsen played Debbie Reynolds' sweetheart in the 1957 film "Tammy and the Bachelor," was the Revolutionary War fighter Francis Marion in the Disney TV adventure series "The Swamp Fox" and had roles in such TV series as "The New Breed" and "Bracken's World."
"I just always worked," he said. "I played a lot of leaders, autocratic sorts. Perhaps it was my Canadian accent."
Nielsen also was captain of the doomed ocean liner in the 1972 disaster movie "The Poseidon Adventure."
All the while he "was a closet comedian," he told The Times in 1991.
Then "Airplane!" changed his career.
Producers-directors-writers Jim Abrahams and David and Jerry Zucker hired Nielsen and other veteran actors Robert Stack, Peter Graves and Lloyd Bridges, all perfectly cast to spoof their own heroic and very serious images.
"I will be forever grateful to them," Nielsen told The Times in 1991. "It is just an amazing roll of the dice. I am so lucky to be a representative of their humor."
Nielsen then was cast in "Police Squad!," which aimed to do to cop shows what "Airplane!" did to disaster movies.
It lasted all of six episodes on ABC, but Nielsen moved on as Drebin to the 1988 movie "The Naked Gun: From the Files of Police Squad!," with George Kennedy, O.J. Simpson and Priscilla Presley among his co-stars. Its success led to two sequels.
"Leslie has the idea to play it maybe not straight but deadly serious," David Zucker told the L.A. Daily News in 1994. "You can take any one performance and just transfer it from a comedy to a drama. There's just no difference — that's what he can do."
Nielsen was born Feb. 11, 1926, in Regina, Saskatchewan. His father was a Royal Canadian mounted police officer and one of his brothers became a deputy prime minister of Canada.
He joined the Royal Canadian Air Force after graduating from high school and after the service studied at a Toronto radio school operated by Lorne Greene — who would become a TV star with the series "Bonanza"— before moving to New York to start working in television.
Nielsen's later movies included "All I Want for Christmas" in 1991, "Dracula: Dead and Loving It" in 1995, "Spy Hard" in 1996 and "Mr. Magoo" in 1997.
He also toured with his one-man show on the life of defense lawyer Clarence Darrow.
Nielsen had two daughters and was married three times previously, according to the Associated Press. A complete list of survivors was not available.