Kasidy Danielle Yates was a freighter captain and latterly the wife of Captain Benjamin Sisko. Yates commanded the Xhosa on freight runs, initially as an independent transporter, but later for the Bajoran Ministry of Commerce. Her primary missions were to export cargo from Bajor to its colonies.

Yates normally arose at 0500 hours and was usually asleep before 0100 hours.

(DS9: "Indiscretion")

Yates was introduced to Sisko by his son Jake, who felt that his father needed a girlfriend. Yates and Sisko shared a common interest in baseball.

(DS9: "Family Business", "Take Me Out to the Holosuite")

As their relationship went on, Yates decided to take an opportunity to work for the Bajorans. This allowed her to move to Deep Space 9 permanently. However, she also used smuggled cargo to the Demilitarized Zone for the Maquis.

In 2372, she unwittingly aided the Maquis in the theft of twelve industrial replicators that were intended for Cardassia. Yates was suspected of working for the Maquis by Odo. Yates was tricked into taking her ship on another smuggling run, drawing a suspicious Captain Sisko and the USS Defiant into the Badlands. She was sent to prison for her actions.

(DS9: "For the Cause")

After her release in 2373, Yates and Sisko picked up where they had left off, with Sisko accepting her back to the station and into his life without a second thought. Yates subsequently returned to work for the Bajorans.

(DS9: "Rapture")

In 2374, Yates agreed to act as convoy liaison officer aboard the Defiant while it served as escort for the PQ-1 convoy, as she knew many of the freighter captains involved with the mission. However, she complained that she had no idea the job would involve writing twenty log entries a day and filling out formal reports for Starfleet every night. She joked that the reason she didn't join Starfleet was because she couldn't do the paperwork. Yates was still present aboard the Defiant when it received a distress call from Captain Lisa Cusak, and she took part in shifts with the Defiant crew in keeping an open communication line to the stranded Captain. However, Sisko felt uncomfortable having Kasidy, a civilian, aboard the Defiant, and she was worried by his unfriendly behavior. He later apologized and promised to make it up to her over dinner.

(DS9: "The Sound of Her Voice")

In 2375, Sisko proposed to Yates, and she accepted, causing much celebration among the Bajoran people, who began to plan a grand wedding for their Emissary.

(DS9: "Penumbra")

Sisko initially backed out of the marriage, having been warned by the Prophets that he and Kasidy could not walk the same path. Sisko decided to ignore the warning and the two were married by Admiral William Ross in a private ceremony on Deep Space 9.

(DS9: "'Til Death Do Us Part")

The first few weeks of their marriage were not all clear sailing, however. Shortly after their wedding, Yates destroyed some of Sisko's home-grown bell peppers in a failed attempt to cheer him up by cooking for him. Sisko attempted to keep Yates and her freighter out of the escalating Dominion War by having the Bajoran Freight and Shipping Authority take her off the active list, much to her annoyance; he later relented.

(DS9: "The Changing Face of Evil")

Later in 2375, Yates discovered that she and her husband were going to have a baby. The pregnancy was unplanned, and Sisko surmised that his last contraception injection must have expired without him returning to the infirmary for another. Yates worried that something might happen to the baby following the Prophets' earlier warning to Sisko that marrying Kasidy would bring him sorrow. Sisko reassured his wife that nothing would happen to their baby, giving her his word as the Emissary.

(DS9: "The Dogs of War")

During a battle with the Pah-wraith possessed Dukat in the Bajoran fire caves, Sisko sacrificed his life to defeat the evil Kosst Amojan and joined the Prophets in the Celestial Temple, leaving Yates and their unborn child behind. Sisko later appeared to Kasidy in a vision, and promised her that he would be back, "maybe (in) a year, maybe yesterday."

(DS9: "What You Leave Behind")