Underground Kingz (UGK) was an American hip hop duo from Port Arthur, Texas, formed in 1987 by Chad "Pimp C" Butler and Bernard "Bun B" Freeman. They released their first major album “Too Hard to Swallow”, in 1992. The duo was featured on hit singles by other artists including "Big Pimpin'" by Jay-Z and "Sippin' on Some Syrup" by Three 6 Mafia.
Pimp C was incarcerated for an aggravated gun assault charge in 2002. Throughout the time of his incarceration, Bun B carried on the UGK name by making numerous guest appearances on songs by other artists, with every appearance either mentioning Pimp C or featuring a "Free Pimp C!" or "Free the Pimp" chant. Many of UGK's peers did the same, and mentioned Pimp C in their own songs with or without Bun B. Pimp C was released from prison in 2005.
Rap-A-Lot Records released Pimp C's solo debut, Sweet James Jones Stories in 2005, and Pimp C founded UGK records. Bun B released his own solo foray, Trill, which opened at #6 on the Billboard Hot 200, and peaked at #1 on Billboard's Top R&B/Hip-hop.
The self-titled “Underground Kingz” debuted at number one on the Billboard 200 in August 2007. Featured guests included Talib Kweli, Too Short, Rick Ross, Z-RO, Three 6 Mafia, Slim Thug, OutKast, as well as hip-hop legends Kool G Rap and Big Daddy Kane on a Marley Marl-produced track titled "Next Up". DJ Paul and Juicy J produced the second single, "International Player's Anthem (I Choose You)". The album got a positive reception both commercially and critically. It received a 4-star rating from Allmusic, and reached #1 on the Billboard Hot 200 album charts.
On December 4, 2007, Pimp C died of an accidental Promethazine/Codeine syrup overdose combined with sleep apnea.