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Former Sen. Fred Thompson, the Watergate investigator-turned-actor-turned national political figure, died Sunday at 73 from lymphoma, with which he had struggled for more than a decade, his family said.

Thompson, a towering, burly man with a deep, Southern-inflected voice, parlayed his fame as a key investigator of the Watergate scandal into a TV and movie career before he was elected to finish the Senate term of Al Gore of Tennessee, who vacated the seat when he became vice president.

Thompson, a Republican, was elected to the seat in his own right in 1996. He ran unsuccessfully for the Republican presidential nomination in 2008.

Related: Fred Thompson Drops Out of 2008 GOP Presidential Race

But it was as an actor — especially as Arthur Branch, the gruff, no-nonsense district attorney of Manhattan, on NBC's "Law & Order" from 2002 to 2007, and as Rear Adm. Joshua Painter in the 1990 movie "The Hunt for Red October" — that Thompson achieved notoriety.

When reporters asked him how he was on law and order as a political candidate, he famously liked to answer: "I'm amazing."

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Fred Thompson speaking at the 2008 Republican National Convention in St. Paul, Minnesota. Reuters — file

Thompson — who often acted under the screen name Fred Dalton Thompson — made the most of his slow-talking, aw-shucks Southern demeanor, but in real life, as in politics, the good-old-boy image concealed a sharp legal mind.

Thompson was assistant U.S. attorney in Nashville, Tennessee, in 1972 when he became campaign manager for Republican Sen. Howard Baker's re-election.

When the Senate appointed a special committee to investigate alleged crimes by the Nixon administration in the 1973 break-in at Democratic National Committee headquarters at Washington's Watergate Hotel, Baker was ranking minority member, and Thompson was hired as Republican counsel.

Thompson was among the first people outside the administration to learn of President Richard M. Nixon's secret Oval Office taping system. It was Thompson who asked Nixon's former deputy assistant, Alexander Butterfield, the question that led to Butterfield's public revelation of the tapes on July 16, 1973.

Thompson was a lobbyist and lawyer for the next decade, until 1983. That's when a book was published about one of his legal clients — Marie Ragghianti, a former chairwoman of the Tennessee Parole Board who was a whistleblower in the scandal that led to the removal of Tennessee's governor from office.

Fred Thompson in an interview on NBC's 'Meet the Press' in 2007. NBC News

The book was turned into a movie, and Thompson was asked to play himself.

Within five years, he was a busy actor, usually playing authority figures, "When Hollywood directors need someone who can personify governmental power, they often turn to him," The New York Times wrote in a 1994 profile.

Thompson was diagnosed with non-Hodgkins lymphoma in 2004. In 2007, as he was preparing his presidential campaign, the cancer returned, but he said it wasn't expected to pose any difficulties. He died Sunday in Nashville surrounded by friends and relatives, his family said.

"He enjoyed a hearty laugh, a strong handshake, a good cigar, and a healthy dose of humility," the statement said. "Fred was the same man on the floor of the Senate, the movie studio, or the town square of Lawrenceburg, his home. ...

"Our nation has lost a servant, Tennessee has lost a son, and our family has lost its rock," it said. "In the days ahead, we ask for prayers of comfort, assurance, and peace."