"Well, tell me what it is and I'll order it for you. It may take some time, but if it exists I'll get it."
"That's just the point, Quark. The program I want doesn't exist. Not yet, anyway."
Kira Nerys was a custom holoprogram commissioned by Tiron, a wealthy business associate of Quark's, who became obsessed with Major Kira Nerys in 2373. After being rebuffed by the real Kira, Tiron offered Quark one bar of gold-pressed latinum and an ornate ring to create the next best thing.
After two failed attempts to capture Kira's likeness – first by trying to lure her into a holosuite, then by trying to take images of her with a holo-imager – Quark finally purchased a high-level decryption protocol to illegally access her personnel file, acquiring her voiceprint, retinal scan, and psychiatric profile. Quark's actions were detected by Odo, but instead of arresting him, he and Kira decided to turn the tables by modifying the program to put Quark's head on Kira's body. Upon seeing who was waiting for him behind gossamer curtains on the four-poster bed, Tiron stormed out of Quark's, swearing that he would ruin Quark for his insult. (DS9: "Meridian")
The program eventually came into the possession of Beckett Mariner, despite Quark's belief that he had deleted it. In 2381, Mariner gave Quark the isolinear chip containing the program in exchange for Quark clearing her bar tab. When Kira became suspicious about the chip, Quark chewed it and ran away. (LD: "Hear All, Trust Nothing")
"Kira" was a combined portrayal of body double Leah Burrough, Armin Shimerman's head, and Nana Visitor's voice. Burrough filled in after Visitor panicked when she had to wear the rubber head, which was filled in with Shimerman's head in post production. (Star Trek: Deep Space Nine Companion, p. 187)