The Old Republic's first expansion pack, Rise of the Hutt Cartel is centered around the rising threat of the Hutt Cartel, which has arisen to challenge the Galactic Republic and the Sith Empire for control of the galaxy. The battle with the Hutts is centered around the planet Makeb, which hides a "powerful secret". Much like the main game, the campaign on Makeb is fully voiced. The expansion raises the level cap to 55, with the leveling from 50 onwards centered around Makeb.
Released on April 14, 2013, those who preordered it prior to January 7, 2013 were allowed early access starting on April 9.
Source: Wikipedia, "Star Wars: The Old Republic", available under the CC-BY-SA License.