Which, of course, he was, including a stint on the Watergate committee, a few years as a lobbyist and, of course, eight years as U.S. senator from Tennessee. He also had a short-lived run for president in 2008.
But you'd be forgiven if you found the real-life Thompson and the movie-made Thompson hard to tell apart.
"Fred was one of the only people that I've met who was truly a renaissance man. Prosecutor, politician, actor, raconteur -- no matter what he did, he did it incredibly well," said "Law & Order" producer Dick Wolf in a statement. "And he was simply a great guy. He will be missed by all those whose lives he touched."
Thompson played District Attorney Arthur Branch on "Law & Order" and its spinoffs for five years.
Scott Glenn, who worked with Thompson on "The Hunt for Red October," also praised his old colleague.
"He brought strength and reality to his work. His love for acting was only superseded by his love for his country," said Glenn in a statement. "I will miss him."
Thompson died Sunday. He was 73.
As an actor, Thompson appeared in such films as "No Way Out," 1990's "Die Hard 2" and "Red October," and "In the Line of Fire." But he was probably best known for his role as "Law & Order's" Branch, joining the long-running show in 2002.
If the original "L&O" D.A., Adam Schiff (Steven Hill), was known for his dyspeptic asides
, Thompson's Branch was fond of down-home Southern sarcasm.
In the movies, Thompson also made use of his matter-of-fact demeanor.
Thompson had a wry response when asked about switching from politics to acting.
"I told people, I had to get into show business in order to get my political views taken seriously," he told The New York Times in in 2005
The rock-ribbed Republican told the Times he was willing to be flexible as an actor. He would even, he said, play a Democrat.
"Of course," he said with a laugh. "I've played a lot worse."