Washington - Long-time columnist and television commentator Robert Novak, known affectionately as the "prince of darkness" for his skepticism and tenacity on the job, died Tuesday morning at the age of 78, according to his home paper the Chicago Sun-Times.

Novak, one of the country's most influential conservative commentators, was most known for his work since the 1960s as a syndicated columnist for the Chicago Sun-Times in Washington and hosting popular television debate shows on CNN.

He died at his home in Washington after a year-long battle with brain cancer, the paper said. He is survived by his wife, Geraldine, and two children.

"No matter what (Novak) had going on, he was always at the ready to help out on stories, and he broke more than his share," said Don Hayne, editor in chief the Sun- Times.

Novak's almost-daily column with the Sun-Times, written together with Rowland Evans Jr, was one of the most influential in Washington circles for decades. But while Novak began his career in writing, he later moved into the new world of 24-hour news television.

Novak became a political analyst for CNN soon after its launch in 1980. He started the debate programme Capitol Gang and later co- hosted Crossfire, a controversial but popular show that pitted Novak's conservative punditry against a left-wing analyst each week.

In his later years, Novak became swirled up in a controversy over the outing of CIA agent Valerie Plame, a scandal that eventually led to the conviction of former vice president Dick Cheney's chief of staff Lewis "Scooter" Libby on charges of perjury and obstruction of justice.

Novak first reported her identity in a 2003 column. Plame's husband, Ambassador Joe Wilson, long claimed her name was leaked by former president George W Bush's administration in retaliation for his criticism of the case for the Iraq invasion.

Novak denied the name was purposely leaked by Bush administration officials. It eventually emerged that his initial source was then- deputy secretary of state Richard Armitage.

Novak was born in 1931 in Joliet, Illinois. He began his Washington political career in 1957 as a reporter for the Associated Press and later the Wall Street Journal.(dpa)