Juan Martinez (born January 13, 1985), better known by his stage name Down AKA Kilo, is an American rapper from Oxnard, California.

Martinez was born in Oxnard; his parents were illegal immigrants from Mexico. Growing up, he listened to Cypress Hill and N.W.A and began rapping at age 13. He made his first recordings at the garage of childhood friend Edward "E-Dub" Rios, who would later become producer of the Power 106 radio show Pocos Pero Locos. He released his debut album California Cowboyz in 2003, and his second album Definition of an Ese in 2007, with two singles from the album, "Lean like a Cholo" and "Definition of an Ese."