In an effort to secure the space station Terok Nor against Bajoran Resistance insurgents, Dukat created a counter-insurgency program which activated a series of pre-programmed events intended to quash any uprising of the station's Bajoran workforce.
As part of this program, Kell secretly added a subroutine to rescind Dukat's command codes, as a precaution in the event Dukat ever tried to abandon Terok Nor himself.
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")
"Dukat, if you are seeing this recording, it means you tried to abandon your post while the station's self-destruct sequence was engaged. That will not be permitted. You have lost control of Terok Nor, disgracing yourself and Cardassia. Your attempt to escape is no doubt a final act of cowardice. All fail-safes have been eliminated. Your personal access codes have been rescinded. The destruct sequence can no longer be halted. All you can do now is contemplate the depth of your disgrace and try to die like a Cardassian."
Legate Kell is briefly mentioned in the Pocket DS9 novels The Art of the Impossible (part of the Star Trek: The Lost Era series) and Fearful Symmetry, the latter of which describes him as being a stocky man with iron gray hair.
The Star Trek: Terok Nor novels Day of the Vipers and Dawn of the Eagles give his first name as "Denig" and recount his career prior to and during the Occupantion of Bajor, from the 2320s until the 2360s. The novels reveal he served as Gul Dukat's superior on both the starship Kornaire and subsequently the space station Terok Nor. The two officers had an adversarial relationship in which Kell often berated Dukat, while Dukat, frustrated by Kell's apparant inept policies concerning the Bajorans, took every opportunity to undermine him. The novels go onto describe a plan by Kell to quash the Bajoran insurgency during the Occupation which ultimately backfires on him.