Jesse Donald Knotts was born in Morgantown, W.Va., on July 21, 1924, the youngest of four brothers. His family life was troubled; Knotts' father twice threatened his mother with a knife and later spent time in mental hospitals, while older brother Earl — nicknamed "Shadow" because of his thinness -- died of asthma when Knotts was still a teenager.

Years later, the actor did not recall his childhood fondly.

"I felt like a loser," he recalled in a 1976 interview with the Los Angeles Times. "I was unhappy, I think, most of the time. We were terribly poor and I hated my size."

Knotts turned to performing in his early teens, doing an Edgar Bergen-inspired ventriloquism act with a dummy he named Danny.

He enlisted in the Army in 1943 and served in the Pacific, receiving the World War II Victory Medal among other decorations. After the war, in 1948, he graduated from West Virginia University with an education degree.

He soon borrowed $100 and moved to New York to pursue an acting career. He auditioned for several radio gigs but was turned down. One of his earliest TV roles was on the CBS soap opera "Search for Tomorrow," where he played Wilbur Peterson — a neurotic young man so troubled he communicated only with his sister -- from 1953-55. It was the only non-comedic role he ever played.

But Knotts did not receive widespread attention until he appeared on Broadway in Ira Levin's 1955 comedy "No Time for Sergeants." Based on Mac Hyman's novel, the play concerned a hillbilly — played by a then-unknown Andy Griffith -- who was drafted into the Air Force. Knotts won plaudits as an overly tense military evaluator.

From 1956-60, Knotts further cemented his reputation on NBC's "The Steve Allen Show," where he would play a character named Mr. Morrison, aka "the nervous man." Interviewed on the street, Morrison was asked whether something was making him nervous and would inevitably offer a terse, anxiety-wracked "No!"

In the meantime, "No Time for Sergeants" was made into a feature film in 1958, with Griffith and Knotts reprising their roles. The two actors kept in touch, and when Griffith signed to do the TV series as a rural sheriff, Knotts half-jokingly suggested that the lawman would need a deputy.

Knotts left "Andy Griffith" in 1965, later explaining that he believed the producers had always intended for the series to last just five seasons. In a 1967 Times interview, he said, "The grind gets to you in television, and that's primarily the reason I'm concentrating on pictures."

Griffith stayed with the program for three years after Knotts' departure, however, and Knotts agreed to revive his role as Fife in a number of guest spots. Even without Knotts, "Andy Griffith" remained popular, and the show was ranked No. 1 in its final season, 1967-68. Episodes remain syndication favorites and still appear in frequent rotation on cable network TV Land.

But many fans now believe "Andy Griffith" fizzled creatively without Knotts' manic energy — a point that even Griffith himself has conceded. On the TV fan site www.jumptheshark.com, one viewer wrote, "When Barney Fife left town, 'The Andy Griffith Show' changed from a television classic to just another 60's TV show."

After "Griffith," Knotts stayed busy, although he never quite matched the success he had seen as Barney Fife. An NBC variety hour, "The Don Knotts Show," premiered in 1970 and lasted just one season. The actor subsequently appeared in several live-action Disney features: as a bumbling bandit in "The Apple Dumpling Gang" (1975), a would-be safecracker in "No Deposit, No Return" (1976) and an auto-racing veteran in "Herbie Goes to Monte Carlo" (1977). He also reprised his role as Fife in "Return to Mayberry," a nostalgic TV movie that delivered enormous ratings for CBS in 1986, and had a recurring role in "Matlock," CBS' courtroom drama starring Griffith.

A self-described hypochondriac, Knotts suffered numerous health reversals in recent years. He developed vision problems that made driving and some other tasks difficult. In the fall of 2003, he injured his Achilles tendon while starring in "On Golden Pond" at the New Theatre in Overland Park, Kansas, and had to wear a brace onstage.

Two of Knotts' three marriages ended in divorce. The first, to Kathryn Kay Metz, lasted from 1947 to 1964 and produced two children, Karen, an actress who co-starred with her father in a 1996 stage revival of "You Can't Take It With You," and Thomas, both of whom survive him. From 1974 to 1983, Knotts was married to Loralee Czuchna. He was married to actress Francey Yarborough at the time of his death.

"He saw poignancy in people's pride and pain and he turned it into something endearing and hilarious," Yarborough, who is also an actress, said in a statement Saturday.

Knotts received a star on the Hollywood Boulevard Walk of Fame in January 2000.

In the foreword to Knotts' 2000 memoir, "Barney Fife and Other Characters I Have Known," Griffith wrote that Knotts personally had little in common with his most famous creation. "Don was not Barney Fife," Griffith wrote. "I know Don to be a bright man and very much in control of himself. As everyone knows, Barney Fife had very little control of himself. In the comedy scenes we did, I was often closer to Don than the camera and I could look at him before we started those scenes, and through his eyes, I could see him become Barney Fife."

Don Knotts (1924)