Ezri Dax () is a fictional character who appears in the seventh and final season of the American science fiction TV series Star Trek: Deep Space Nine. Portrayed by Nicole de Boer, she is a counselor aboard the Bajoran space station Deep Space Nine. The character is a member of the Trill species, and is formed of both a host and a symbiont—referred to as Dax. Ezri was introduced to the series following the death of the previous Dax host, Jadzia (Terry Farrell) at the end of season six. It had been the producers' intention to introduce a new female character bearing the symbiont in order to ensure that Nana Visitor as Kira Nerys was not the only female member of the main cast. There were difficulties in casting initially, and the character changed from one who was intended to be "spooky" to one who was struggling to deal with all her previous personalities as a result of unexpectedly taking on the Dax symbiont. De Boer was not considered for the part until co-producer Hans Beimler suggested that she should submit an audition tape, which resulted in her invitation to meet with the producers in Los Angeles and in her gaining the role.
The character made her appearance in the first episode of the seventh season, "Image in the Sand". The character continued to appear throughout the final season of the series, with her final appearance in the series finale, "What You Leave Behind". Her character stepped into the void left by Jadzia amongst the crew, but found that she had to redevelop those previous relationships and learn to get along with Jadzia's widower, Worf (Michael Dorn). During the course of the season, Ezri becomes less nervous of her role with the crew. She learns from the Dax symbiont and becomes involved romantically with Dr. Julian Bashir (Alexander Siddig).
The fan reaction to the character was reported as positive, but several of the Ezri-centric episodes came in for criticism, with producer Ira Steven Behr apologising to de Boer for "Prodigal Daughter" – an episode described as "just a mess" by writer Ronald D. Moore. The relationship between Ezri and both Worf and Bashir was described as one of five "great geek TV love triangles". The inclusion of the character was criticised on the internet, with Ezri being referred to as both an "ill-conceived idea" and a "replacement Dax".
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