Kell was a male Cardassian officer in the 24th century Cardassian military. He became a legate in the Cardassian Central Command and, in the 2360s, was Gul Dukat's commanding officer during the Occupation of Bajor.
As part of Gul Dukat's counter-insurgency program, Kell secretly added a subroutine to rescind Dukat's command codes, as a precaution in case Dukat ever tried to leave Terok Nor during a worker rebellion.
Dukat did not find out about Kell's modification until 2371, when the program was activated on Deep Space 9. Kell's recording played and his final remark to Dukat was "try to die like a Cardassian". (DS9: "Civil Defense")