Jadzia Dax is one of the main characters in the Star Trek Deep Space Nine series. She is a commanding officer and an officer of science.
She is in symbiosis with a symbiont named Dax who lives extremely long. The two forms a “joint Trill”.
The Trills are a humanoid breed with an Alpha strain (with a bump on the skull) and a Beta strain (with stains on the tampers).
The symbiotes live in caves on the same planet and are guarded by a portion of the population that cares for them until they get a host.