JAMES ARNESS, who played Marshal Matt Dillon on the TV show "Gunsmoke" for 20 years, died Friday of natural causes, he was 88 years old.

"Gunsmoke" is tied for the record of longest-running primetime drama with the original "Law & Order"... which ran from 1990 to 2010.

"Gunsmoke" was on the air from 1955 to 1970... but it also spawned several TV movies in the '80s and '90s making it, as Arness once claimed, the only show to air in five different decades.

"The Simpsons" actually ran longer.  It's been on the air for 22 seasons and counting... but it's an animated comedy series.

Plus, there were 635 episodes of "Gunsmoke" ... while neither of the other two shows have reached 500.  ("The Simpsons" still could, of course.)

In addition to Matt Dillon, James Arness was also famous for playing the monster in the 1951 sci-fi classic, "The Thing From Another World"(Which was remade as "The Thing" in 1981, starring Kurt Russell.)

Arness was a World War 2 vet and the older brother of "Mission:  Impossible" star PETER GRAVES, who died last year.