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Torias Dax was a joined Trill in the 23rd century. Torias was the fifth host of the Dax symbiont.
Shortly after being joined, Torias Dax married Nilani Kahn, whom he had met when both were initiates.
Torias attempted to climb Betazed's Mount Traxanaxanos three times before giving up the attempts. (DS9 - Rebels novel: The Conquered)
Torias was a pilot, and died in a shuttlecraft accident in 2284. Records of the Trill Symbiosis Commission, however, said Torias survived in a comatose state an additional six months, a falsehood meant to cover-up the subsequent joining of Dax to Joran. (DS9 episodes: "Equilibrium", "Facets", "Rejoined")
There are two contradictory non-canon stories detailing Torias' shuttle accident: "Infinity" in The Lives of Dax, and "Trek" in Strange New Worlds 8.