The 2399 killing of Dahj, a synthetic daughter of Data, whose death led Jean-Luc Picard to search for her twin sister Soji.
Dahj was one of a pair of synthetic sisters created from Data's positronic neurons, living as an ordinary young woman who did not know she was artificial. In 2399 Romulan agents attacked her apartment, and her hidden combat abilities awoke. Driven by visions, she sought out Jean-Luc Picard at his vineyard.
The agents caught up with them, and Dahj was killed in the fighting. Her death convinced Picard that she had a twin, Soji, who was also in danger. His search for Soji brought him back into service and set the events of the Coppelius incident in motion.