Etana
Etana was a Ktarian female who met and seduced William T. Riker on Risa in 2368. 

She tricked him into bringing an addictive, mind controlling game aboard the , as part of a massive plot to take control of Starfleet. 

She nearly succeeded in taking over the starship but, fortunately, her plan failed when Wesley Crusher learned the truth about what she was up to and was able to reactivate Data – who had been disabled before the game was widely dispersed throughout the ship as the only person who would have been immune to its effects – allowing Data to restore the crew to their normal selves and allowing them to capture her vessel. ()

Appendices

Background information
Etana was played by actress Katherine Moffat, and photo doubled by Diane York.

According to the final draft of the script, Etana was "alien, gorgeous, with a full, flowing mane of hair;" additionally, the script also indicated that her last name was Jol.

The character was never specifically identified as Ktarian in the episode, where Etana only spoke of the Ktarians in third person. But Etana is identified as Ktarian in reference and background materials, including Star Trek: Aliens & Artifacts (p. 117), , and StarTrek.com.  

For more information on the discrepancies associated with Ktarians, see the full analysis at .

Apocrypha 
According to the Star Trek: The Next Generation - Player's Guide, Etana Jol turned herself in to Ktarian authorities and agreed to testify against her superiors in exchange for immunity. Afterwards, she became the public relations officer for a chain of Ktarian resorts, but there are rumors that she's planning to embark on a political career.

External link
 
de:Etana Jol
Ktarians