West Wing colleagues have paid tribute to actor John Spencer, who died of a heart attack in Los Angeles, just four days before his 59th birthday.
Spencer described acting as "my escape, my nourishment"
Spencer was best known for his role as Leo McGarry, chief of staff to the US president on hit series The West Wing.
He was "one of those rare combinations of divinely gifted and incredibly generous," said co-star Richard Schiff, who played Toby Ziegler on the show.
Aaron Sorkin, creator of the political series called Spencer "brilliant".
"John was an uncommonly good man, an exceptional role model and a brilliant actor," said Mr Sorkin, in a joint statement with Tommy Schlamme, one of the original executive producers on the NBC show.
"We feel privileged to have known him and worked with him. He'll be missed and remembered every day by his many, many friends."
Executive producer John Wells added his own tribute: "John was a wonderful actor, a pleasure to work with and a true gentleman, but most important, a generous and gracious friend," he said in a statement.
The seventh series of the political drama is currently being shown in the United States.
"There are very few personal treasures that you put in your knapsack to carry with you for the rest of your life, and he's one of those," said Schiff, of his co-star Spencer.
Co-star Schiff (far right) called Spencer "divinely gifted"
Actress Allison Janney, who plays CJ Cregg on the series, described Spencer as a consummate professional actor. "Everyone adored him," she said.
"We have all lost a dear, dear brother," added co-star Bradley Whitford, who plays long-running character Josh Lyman.
Spencer, 58, one of the principal actors in the West Wing ensemble, was nominated as best supporting actor at the Emmy awards each year from 1999 to 2004, winning the award in 2002.
Admired for a string of performances on the big and small screen playing no-nonsense bureaucrats, he was Mr Sorkin's first choice to play Leo McGarry.
"I said to the casting director, 'We need someone like John Spencer'," Mr Sorkin recalled. "And the casting director said, 'What about John Spencer?' And I said, 'We will never get John Spencer'. "
Spencer played chief of staff to Martin Sheen's President Barlet
Spencer accepted the role and made it his own.
Both the character and the actor were recovering alcoholics with a passion for hard work.
Like Spencer, his on-screen persona suffered a heart attack in the sixth season of the show.
But in a cruel twist of fate Leo McGarry was to recover sufficiently to appear in the new series.
Schiff said Spencer had been struggling with health issues, but appeared to have recovered. The actor died less than a day after he checked into a Los Angeles hospital with a bad cold, according to his publicist.
Spencer had already appeared in half of the 14 episodes of the current season. Filming was halted for the holidays, but the remaining episodes were scheduled to be shot in January.
Writers and producers for the series are expected to gather this week to decide how to continue, a studio spokeswoman said.
At its peak The West Wing - currently showing on More Four - was one of the US TV's most popular series, but the much-praised drama has struggled to maintain its place in the ratings.
It is already thought the current seventh season could be the show's finale.