The Castellan of the Cardassian is the elected head of government for the Cardassian Union in the time following the Dominion War. (DS9 novel: Cardassia: The Lotus Flower) This position first existed under the auspices of the First Hebitians, and was a democratically-elected position. The last Castellan was deposed in the late 19th century (Earth reckoning) in a coup led by revolutionary Tret Akleen, after which the rule of Central Command and soon the Obsidian Order was instated. Civilian interests were represented in name only by the Detapa Council. (Star Trek: Sigils and Unions--"Point of Divergence")
In 2376, Alon Ghemor was elected as Castellan, re-establishing the office for the first time in five centuries. (DS9 novels: A Stitch in Time, The Never Ending Sacrifice; Star Trek: War Aftermath Episode 1: The True Way; Star Trek: Sigils and Unions--"A Weaver of Lives")
Sigils and Unions: Catacombs of Oralius continuity
In the Sigils and Unions: Catacombs of Oralius universe, Akleen's revolution never took place. Instead, the First Hebitians reformed into the Cardassian Theonomy, maintaining the position of Castellan, but introducing changes to the legislative and judicial branches of government to better balance the executive power. The Castellan typically had a clergy adviser, known as Guide to the Castellan; in some cases, the Guide and the Castellan worked so closely that they almost seemed to be a single governing unit. (Sigils and Unions: Catacombs of Oralius--"Point of Divergence")
The last known Castellan elected to office before the Bajoran invasion was Shiron. Though Shiron tried a number of desperate measures to fend off the threat, instituting an emergency draft of all men over the age of twenty-four, and transmitting an emergency plea to the Federation for assistance, which was summarily rejected on grounds that the both parties framed the conflict in religious terms (even though the petition was by the non-aggressor) and therefore in their opinion, a Prime Directive matter.
Shiron's fate once the Bajorans landed troops is unknown. Since that day in 2525, no further elections have been held due to Cardassia's conquered status. ("The Desolate Vigil")