WASHINGTON (CNN) -- Conservative columnist and former CNN "Crossfire" co-host Robert Novak has died after a yearlong battle with cancer, his family said Tuesday. He was 78.

Robert Novak was a syndicated columnist who was a regular on CNN for 25 years.

Novak died at home, over a year after doctors diagnosed him with a malignant brain tumor in August 2008.

He was dubbed "The Prince of Darkness" by friends for his pessimistic persona, and he used the nickname as the title of his 2007 memoir.

However, Sam Feist, CNN's political director, said the dour visage masked a "warm-hearted guy" who "cared a lot about the people who worked for him." Watch how Novak will be remembered »

"If you were a friend of Bob Novak's, you couldn't have a better friend," Feist said.

Jim Walton, president of CNN Worldwide, said the network was saddened by the death of "a journalist of the old school, hard-working, practical and passionate about our profession."

"From its earliest days and for some 25 years, Bob shared generously with CNN and with CNN viewers his authority, credibility, humor and towering presence," Walton said in a statement. "We're grateful to have worked alongside him and send our respect and sympathy to his family."

Novak was a veteran columnist for the Chicago Sun-Times and a regular commentator for CNN for 25 years, beginning when the network launched in 1980.

For most of that time, he was a co-host of the political debate program "Crossfire." But he also hosted a show with his longtime column co-author, Rowland Evans, and appeared as a panelist on shows like "The Capital Gang" and on PBS' "The McLaughlin Group."

Novak got his first newspaper job in 1948, when he was still in high school.

Senate Minority Leader Mitch McConnell, R-Kentucky, said Novak had "the kind of keen insight that can only be gained through years and years of dedication to a craft."

"He was a Washington institution who could turn an idea into the most discussed story around kitchen tables, congressional offices, the White House and everywhere in between," McConnell said in a written statement.

Novak served in the Army during the Korean War before turning to the news business, eventually starting his column with Evans at the now-defunct New York Herald-Tribune in 1963.

In 2003, he found himself at the center of the scandal over the exposure of CIA agent Valerie Plame Wilson, when he published a column revealing her CIA status days after her husband challenged a key Bush administration justification for the invasion of Iraq.

While staunchly conservative, Novak opposed the invasion and was frequently critical of the Bush administration. He cooperated with prosecutors and was not charged in the leak case.

The scandal ultimately led to the conviction of Vice President Dick Cheney's chief of staff, Lewis "Scooter" Libby, on charges of perjury, obstruction of justice and lying to investigators probing the leak.

Novak later testified that the leak began with then-Deputy Secretary of State Richard Armitage and was confirmed by Karl Rove, who was then President George W. Bush's top political adviser. Both men cooperated with the investigation, and neither was charged. iReport.com: Share memories of Novak

Novak was born to a Jewish family in Joliet, Illinois, on the outskirts of Chicago, but later became a devout Roman Catholic. He took up skydiving in his early 70s and was a passionate sports fan. He also once appeared as an extra in a Washington opera production.

In an editorial published with news of Novak's death, the Sun-Times said Novak's columns "were marked by his determination to dig out new information."

"He combined that with sharp analysis, insightful commentary and passion about the issues facing the nation to emerge as a brawling contestant in the great national debates of his era," the newspaper said.

Veteran Democratic consultant and on-air sparring partner James Carville said Novak "had the best sources in the Republican Party," making his weekly column a must-read for political insiders.

"What you saw on television was an ideological guy, a fire-breathing right-wing guy," Carville said. But Novak "still had the sort of ethos of the reporter."

Novak left the network in 2005 after an on-air blowup with Carville, who had been needling him over the CIA leak case. CNN suspended Novak, who apologized for using the word "bullsh*t" on air, and he resigned at the end of the year.

"I want to thank CNN for making this network available to me for 25 years," he said at the time. "Never censored me once, ever, and I said some outrageous things. And it was a wonderful opportunity for me."

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