Steth was one of many victims of an unknown lifeform with the ability to switch DNA with humanoids by use of selected DNA exchange. Steth was left with the DNA of a female humanoid, the previous victim, when he encountered this lifeform.

Steth later rescued Tom Paris, now with his original DNA, from the Benthan Guard in the Kotaba Expanse. Together, they made their way to USS Voyager, where they captured the impostor. (VOY: "Vis à Vis")

Steth was played by Dan Butler in his original body and by Mary Elizabeth McGlynn in Daelen's body.
According to a deleted lines from the script, the impostor has switched with Steth (leaving him as a female) for almost a year ago, and Steth, as Daelen, had just spent eight months in prison for the crimes the impostor has committed as Daelen.
Though not explicitly stated to be a Benthan, it is evident that the impostor continued to live the life of his present appearance. Star Trek Online models its Benthans after him.
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