Kelvin Mercer (born August 17, 1969, The Bronx, New York) is a rapper, producer, and one-third of the hip hop trio De La Soul. He is known more famously by his alias Posdnuos, or simply Pos. He was born in the Bronx, New York and grew up in East Massapequa, New York.

Mercer and David Jude Jolicoeur were childhood friends. They met Vincent Mason in the early 1980s while attending Amityville High School in Long Island, New York. Mercer's father was a jazz fan.