James Arness is best known for his role as Marshal Matt Dillon in 'Gunsmoke,' one of the longest-running prime-time series in network TV history. He was a towering symbol of frontier justice in the series that broke the mold for TV westerns.James Arness, the towering actor best known for portraying Marshal Matt Dillon, the strong and commanding symbol of frontier justice on the landmark TV western series "Gunsmoke," died Friday.