Turrel

Legate Turrel is perhaps best known as the Cardassian Union's negotiator in the 2371 Bajoran-Cardassian Treaty. Prior to that attempted to influence Cardassian-Maquis relations, although he was unable to sustain this effort beyond a single mission that ended in failure. 

Maquis relations
In the months prior to fellow legate Tekeny Ghemor's arrest, Turrel was among those who pushed for a new tactic in dealing with the Maquis problem: circumventing the official Federation colonists' representatives and taking the Cardassian case directly to the people of the ceded DMZ colonies. The idea was to demonstrate greater restraint towards the former Federation citizens and reward peaceful conduct with an influx of provisions and supplies the Maquis could not provide.

This idea was rather tepidly received by Central Command; while they agreed to try it, junior gul Tayben Berat was sent as the Cardassian envoy rather than Turrel or even a more experienced gul like Akellen Macet. In truth, Berat may well have proven up to the task if given the chance to complete it--but an assassination attempt proved near-fatal to Berat due to prior neurological damage.

Berat, for one, maintained faith in his abilities despite the disabling injury, and appealed the standard discharge orders for one in his physical condition--a move that could have gotten him executed. He also asked for a second chance on Volan III, believing his return would send a strong signal to skeptics as to Cardassia's willingness to pursue peace. Together with Legate Ghemor, Turrel succeeded in overturning Berat's discharge and allowing him to retain his command. Unfortunately, the two legates' influence was not strong enough to keep Central Command from ending its experiment and tasking Gul Evek with dealing out reprisals to the citizens of Volan III. (The Thirteenth Order)

Dissident ties?
Turrel had some degree of rapport with fellow legate Tekeny Ghemor, though it is unknown whether Turrel shared Ghemor's ties to the Cardassian dissident movement. Whatever the case, the Obsidian Order never charged him with anything and after Ghemor's downfall, Turrel retained his position. (: The Thirteenth Order, "A Weaver of Lives")

Peace negotiations
Perhaps because of his attempts to defuse the Maquis situation, Turrel was initially contacted by Vedek Bareil Antos; the two quickly developed a good relationship. Though interested in peace, Turrel proved a shrewd negotiator determined to give up only the minimum of concessions required to ensure the acceptance of the treaty on both sides--particularly Central Command, which would not be kindly disposed towards any deal that could possibly be viewed as favoring the Bajorans.

Turrel determined to continue negotiations following an attack that mortally wounded Bareil. While Bareil had been adept at parrying his counterpart's diplomatic moves, his replacement, Kai Winn Adami, lacked this skill and rapport in dealing with Turrel and the negotiations nearly fell apart. Only with assistance from the dying Bareil was Winn able to complete negotiations with Turrel and sign a treaty. 

Dukat's revenge
Because of his role in normalizing Bajoran-Cardassian relations, Legate Turrel, along with civilian leader Kotan Pa'Dar, was one of the first people executed following Gul Dukat's Dominion-backed rise to power in 2374. (: "A Weaver of Lives")