Columnist Robert Novak, one of Washington's most well-known political commentators, has died after a battle with brain cancer. 

He was 78. 

Novak died early Tuesday morning at his home in Washington. He had been a columnist for the Chicago Sun-Times for decades as well as a prominent television commentator. 

In recent years, he was perhaps best-known for being the first to publish the name of CIA operative Valerie Plame. He came under criticism from many for that column, which Novak said began "a long and difficult episode" in his career.

But while Novak for years carried the nickname of "Prince of Darkness" with pride, colleagues said his reputation was that of a hard-working and even-handed reporter. He was a columnist but strived to report original material in those columns. 

"More than anyone else in journalism I admired the way he operated," the Weekly Standard's Fred Barnes said. "He was a conservative but he was always very tough on Republicans as well as Democrats, and he terrified a lot of politicians in town." 

Novak was diagnosed with a brain tumor in July 2008, less than a week after he struck a pedestrian in downtown Washington with his Corvette and drove away.

Novak, editor of the Evans-Novak Political Report, was well known as a co-host of several of CNN's political talk shows, where he often jousted with liberal guests from 1980 to 2005 -- among the shows was "Crossfire." He was also an occasional contributor to FOX News. 

"I had a terrific time fulfilling all my youthful dreams and at the same time making life miserable for hypocritical, posturing politicians and, I hope, performing a service for my country," Novak wrote in his memoir, "The Prince of Darkness: 50 Years Reporting in Washington." 

"He loved being a journalist, he loved journalism, he loved his country and his family," his wife Geraldine Novak told The AP. 

Novak wrote in his book about often giving politicians the choice of being a source or a target, a strategy that often produced scoops for his column. 

Among those scoops included a 2003 column in which he outed Plame as a CIA agent. The article was published eight days after Plame's husband, Joseph Wilson, said the Bush administration had twisted prewar intelligence to exaggerate the Iraqi threat of nuclear weapons. 

Citing two Bush administration officials, Novak revealed Plame worked for the CIA on weapons of mass destruction. That blew her cover as a CIA operative and led to the investigation of who leaked that information, and eventually to the conviction of I. Lewis "Scooter" Libby, Vice President Dick Cheney's former chief of staff. 

Libby was convicted on perjury charges, though, and not implicated as the leak. Former Deputy Secretary of State Richard Armitage later admitted to being the source of the leak. 

Libby's prison sentence was later commuted by President Bush. 

Born and raised in Joliet, Ill., Novak began his career in journalism in high school as a sports stringer for the Joliet Herald-News, then worked at the Champaign-Urbana Courier while attending the University of Illinois.

He was born to a Jewish family, but converted to Catholicism in 1998. 

The Associated Press contributed to this report.