Lieutenant Commander Jadzia Dax

Dax was a Trill. The Trill (or Trills) is the name of a humanoid species native to the planet Trill. A small percentage of the Trill population co-exists with a sentient symbiotic organism known as a symbiont inside their bodies. The resulting joined Trills have personalities which are a synthesis of the two beings including the memories, and to some extent the personalities, of the previous hosts of the symbiont. This way, the joined being gains all the skills and occupations of the previous hosts