From Wikipedia:
The C/K was the name for Chevrolet's full-size pickup truck line from 1962 until 1998 and GMC's full-size pickup line from 1962-1988. The first Chevrolet pickup truck appeared in 1924, though in-house designs did not appear until 1930. "C" trucks had two-wheel drive while "K" models had four-wheel drive. The C/K light-duty pickup was replaced with the GMC Sierra in 1988 and the Chevrolet Silverado in 1999; the Chevrolet Silverado HD and GMC Sierra HD heavy-duty pickups followed in 2001.