(CNN) -- George Jones, the country music legend whose graceful, evocative voice gave depth to some of the greatest songs in country music -- including "She Thinks I Still Care," "The Grand Tour" and "He Stopped Loving Her Today" -- has died, according to his public relations firm.
Jones, 81, died Friday at Vanderbilt University Medical Center in Nashville, the public relations firm said. He had been hospitalized since April 18 with fever and irregular blood pressure.
Jones' career was marked by a tumultuous marriage to Tammy Wynette and bouts with alcoholism that led to occasional concert cancellations. (One of his nicknames was "No-Show Jones"; after he got clean, he puckishly used "No-Show" on his license plates.)
Waylon Jennings once wrote a song that said, "George might show up flyin' high, if George shows up at all/But he may be, unconsciously, the greatest of them all."

In a statement, Merle Haggard said, "The world has lost the greatest country singer of all time. Amen."
Jones, nicknamed "The Possum" for his resemblance to the animal, was born in 1931 in east Texas. His early life was marked by poverty and a violent, alcoholic father. Young George taught himself to play guitar, and by the time he was a teenager he was singing on the streets and in the clubs of Beaumont, Texas, not far from his birthplace of Saratoga.
After a quick marriage and service in the Marines, Jones was discovered by Starday Records co-owner Pappy Daily, who guided his early career. Jones' first single, 1954's "No Money in This Deal," failed to chart, but 1955's "Why, Baby, Why" was a hit. By 1959, Jones had moved to Nashville and recorded his first No. 1, "White Lightning."
Jones' early hits, such as "Lightning," "The Race Is On" and "Root Beer," were in a high-powered, rockabilly mode, but he found his biggest success as a crooner. Ensuing years were marked by such songs as "Things Have Gone to Pieces" and "A Good Year for the Roses," which highlighted broken or thwarted romance and the kind of longing that suggests late, lonely nights in bars.
It was a life that Jones started knowing all too well.
His second marriage, to Shirley Corley, was marked by frequent benders. Jones recalled one that became legend: He had been drunk for several days, and Corley hid the keys to all of their cars. However, he pointed out, she'd forgotten one vehicle: their lawnmower. They lived eight miles from a liquor store but that didn't stop Jones.
"I imagine the top speed for that old mower was five miles per hour," he recalled in his 1996 memoir, "I Lived to Tell It All." "It might have taken an hour and a half or more for me to get to the liquor store, but get there I did."
Jones and Corley divorced in 1968. A year later, he married Wynette, one of Nashville's biggest names. The two had a number of huge hits together, but the strain of their marriage was indicated in song titles such as their "We're Gonna Hold On" and the Jones solo song "We Can Make It." (One of Wynette's singles was called "Kids Say the Darnedest Things"; one of those "things" was "I want a divorce.")
"By now, the couple's marriage was becoming a public soap opera, with their audience following each single as if they were news reports," wrote CMT.com in its Jones biography.
Wynette filed for divorce in 1973, reconsidered and then filed again two years later. This time it stuck. However, though the couple were divorced, they continued to sing together for years afterward. Wynette died in 1998.
Jones' life went into a tailspin. He started using cocaine and missing shows more frequently, 54 in 1979 alone, according to CMT.com. His weight dropped from 150 to 100 pounds. He entered rehab but left after a month.
And yet at this time he recorded perhaps his greatest song, 1980's "He Stopped Loving Her Today," the tale of a man who continued pining for his lost love many years after she left him. The song, written by Bobby Braddock and Curly Putnam, has been voted the greatest country song of all time in a Country Music Magazine poll.
Jones continued to struggle in the early '80s -- once leading police on a car chase in Nashville -- but with the help of his fourth wife, Nancy Sepulvado, he got clean. Though his hit-making slowed down, mainly thanks to changing tastes in country music, he became a revered elder statesman, often credited as an influence by generations that followed. He paid tribute to his own and preceding generations in a 1985 hit, "Who's Gonna Fill Their Shoes."

Other singers stood up for Jones. At the Country Music Association Awards in 1999, Jones was asked to shorten his hit song "Choices." He refused and boycotted the honors. But at the awards, Alan Jackson cut his own song short and went into "Choices," giving Jones his due.
"Not everybody needs to sound like a George Jones record," Jackson once said in an interview, according to The New York Times. "But that's what I've always done."
His singing remains a model.
"There aren't words in our language to describe the depth of his greatness," Vince Gill said in a statement. "I'll miss my kind and generous friend."
Jones, a member of the Country Music Hall of Fame, was honored by the Kennedy Center in 2008 and received a Grammy Lifetime Achievement Award in 2012.