Trill (Star Trek)

Dax is a character in the fictional Star Trek universe. It is a Trill symbiont—a life form that lives inside humanoid hosts. The first appearance of a Trill was in the episode "The Host" from the fourth season of Star Trek: The Next Generation; in that early version, the personality of the being was entirely that of Odan, the symbiont within the host, whereas the personalities of the Trills in Star Trek: Deep Space Nine are a blending of the symbiont Dax and its sequential Trill hosts. Two of Dax's hosts, Jadzia Dax and Ezri Dax, appear as major characters in Star Trek: Deep Space Nine. Others are only seen in flashbacks and when taking over others' bodies in the DS9 season 3 episode "Facets". Dax's hosts also appear in spin-offs such as Star Trek: The Human Frontier and The Lives of Dax.

Throughout the franchise's timeline, Dax has been joined with four men and five women, living for more than three hundred years in total. Dax has been present for many important events in Star Trek history, such as the negotiation and signing of the Khitomer Accords (while joined with Curzon), the discovery of the Bajoran wormhole (while joined with Jadzia), and the end of the Dominion War (while joined with Ezri).

Lela Dax is the first host of the Dax symbiont. Lela appears in the "Facets" Deep Space Nine episode where her consciousness takes over the body of Kira Nerys (Nana Visitor) at Jadzia's zhian'tara ceremony. She is the first Dax incarnation to which Jadzia speaks. Lela is shown as very sociable and easy-going. She comforts Jadzia and dispels her worries as Jadzia was anxious of what she might experience at the ceremony. When talking about herself, Lela says she was one of the first women to be elected to the Trill legislature. She says she took the habit of clasping her hands behind her back to curb excessive hand gesturing while speaking publicly. Jadzia finds she has inherited this behavior.

...
Wikipedia