David Letterman delivered a fiery rant against CBS and parent company Paramount for cancelling Stephen Colbert’s “Late Show,” calling the decision “gutless” and “pure cowardice” as he labeled his successor a martyr of the network.

While ratings for Colbert's show have declined over the last decade, the program has consistently achieved the highest views of any show in the 11:35 p.m. hour, outdrawing ABC's "Jimmy Kimmel Live" and NBC's "The Tonight Show Starring Jimmy Fallon," according to Nielsen.

David Letterman took aim at his former employer, CBS, over the cancellation of 'The Late Show With Stephen Colbert.