Deep Space Nine was the third of five Star Trek shows. It was the first, and only, Star Trek series that was set on a space station. It was also the only Star Trek series to have a commanding officer that was African American.
The characters of Deep Space Nine can be divided into three categories. First, there are the regular characters. These are the characters whose names appear in the opening credits and who appear in over 100 episodes (with the exception of Ezri Dax who was only in the seventh season). The second tier includes recurring characters that appeared in multiple episodes (anywhere from 3 episodes up to 91 episodes). The third group is the characters that were seen in less than three episodes.
The show's regular cast was made up of eight characters in the first three seasons and nine characters in the last four seasons. Most of the characters were military personnel and a few were civilians.
The Sisko Family
The station's commanding officer was a human Starfleet commander named Benjamin Sisko. Not long after his arrival to DS9, Commander Sisko discovered a stable wormhole that the Bajoran people referred to as the Celestial Temple. Sisko's discovery of the wormhole confirms a Bajoran prophecy that names Sisko as the Emissary of the Prophets. (The Prophets are the Bajoran gods.)
At first, Sisko did not like being seen as a religious icon, but as his time on DS9 continued he grew to love this role and took it quite seriously. His status as Emissary caused him problems with the Bajoran spiritual leader, Kai Winn, who was jealous of his communion with the Prophets and did not like having to share her role as Bajor's spiritual leader.
Jake Sisko was the commander's son and lived on the station with his father. Jake was the best friend, and eventual roommate, of a young Ferengi named Nog. Jake was a talented writer. He chose to pursue a career in writing instead of joining Starfleet, like his father hoped he would. Jake's first official writing job was as a reporter during the war against the Dominion. When Commander Sisko was promoted to captain, Jake had the privilege of placing the fourth pip (the rank insignia) on his father's collar.
Kira Nerys
Major Kira was the station's first officer as well as the Bajoran/Federation liaison. She was a tough woman who had grown up fighting for Bajoran independence during the Cardassian Occupation. She was very serious about her faith and would often butt heads with Kai Winn, who was more concerned with her own ambitions than she was with the spiritual well being of the Bajoran people. After Jadzia's death in season six, Capt. Sisko left DS9. Major Kira took command of the station and was soon promoted to colonel.
Dr. Julian Bashir
The Chief Medical Officer was Dr. Julian Bashir. At the start of the series, Julian was young and cocky and would talk about wanting to practice, what he called, frontier medicine. He had a tendency to annoy those around him but by the end of the series had managed to become very close friends with several members of the crew, especially Chief O'Brien. In the later half of the series, it was discovered that Bashir's genius was due to his having undergone an illegal procedure, known as genetic resequencing, when he was a child. By the end of the series, Bashir was a more serious, and somewhat cynical, character compared to the young idealistic man that first joined the crew of DS9.
Miles O'Brien
Chief Petty Officer Miles O'Brien was transferred from the USS Enterprise to serve as the Chief of Operations on Deep Space Nine. The Chief was a skilled engineer who managed to successfully integrate Federation technology into the formerly Cardassian space station. Chief O'Brien was a highly decorated member of Starfleet who had already served for 22 years by the time he began his assignment on DS9. He was married to a botanist named Keiko and had two children. He was also the best friend of Dr. Bashir.
Jadzia Dax
Jadzia Dax is the station's science officer as well as Sisko's close friend and advisor. She is a member of a joined species known as Trill. Dax is a centuries old symbiont that lives inside of Jadzia's body. Jadzia is the eighth Trill to serve as host to Dax. As a joined being, Jadzia has all the memories and knowledge of all of the previous hosts, including Sisko's mentor Curzon Dax. While Jadzia is only 28 at the start of the series, Dax is actually over 300 years old. In season six, an insane Gul Dukat kills Jadzia and the Dax symbiont is sent back to Trill to be joined with a new host.
Odo
Odo was a shape shifter who served as the station's Chief of Security. When the series began, Odo did not know where he came from. As the series progressed, Odo discovered that he came from a planet in the Gamma Quadrant and that he was a member of a race known as the Founders. While he wore a Bajoran uniform he did not have an official rank. Captain Sisko usually referred to him as "Constable". Odo was a stickler for order and precision. He didn't believe in using weapons to do his job, which he was incredibly good at. Odo was so good at his job that the station's residents would sometimes place bets on how long it would take him to solve a case.
Quark
One of the businesses in the station's Promenade was Quark's Bar. It was owned and operated by a Ferengi named Quark. Apart from being a business owner, Quark was the station's resident scoundrel. The Ferengi are capitalistic and greedy and Quark was no exception. Though Quark frequently tried to make money in illegal ways, he still had a conscience. When he was involved with his cousin Gaila's weapons business, Quark played the role of host. At one of the business meetings, the client spoke about wanting weapons that would kill 28 million people. Quark's love of money took a backseat when his conscience kicked in, telling him that this was wrong.
Worf
Lt. Worf was a Klingon warrior who served for several years on the USS Enterprise as Chief of Security. After the destruction of the Enterprise D, the recently promoted lt. commander was transferred to Deep Space Nine. Worf's new assignment was to provide his expertise as Starfleet's only Klingon officer during a time of conflict with the Klingon Empire. Worf remained on DS9 and became the station's Strategic Operations Officer. Worf married Jadzia Dax in season six.
Ezri Dax
Station counselor Lt. Ezri Dax is the second Starfleet officer to serve on DS9 after being joined with the Dax symbiont. She joined the crew in season seven after Jadzia's death in season six. Ezri was the complete opposite of Jadzia. Where Jadzia was confident and strong, Ezri had self-esteem and confidence issues, partly due to having been joined. Unlike Jadzia, Ezri did not go through the years of training and preparation required to be joined. Ezri was chosen because it was the only way to save the life of the dying Dax symbiont when it was being returned to Trill after Jadzia's death. At the end of the series, Ezri was one of the few crewmembers to remain on DS9.
For information on the recurring characters, see my Helium article Guide to the Recurring Characters of Star Trek: Deep Space Nine. For more information on the aliens, ships and story lines of Star Trek Deep Space Nine you can visit the Star Trek library at startrek.com.