Collaborator
A collaborator was an individual who was, almost always, willing to serve or sympathize with the people who conquered their lands. For this, they were often hated by their own.

On Kaminar, Kelpien priests were described as unwitting collaborators due to their enforcement of the grip of the Ba'ul on their Kelpien prey. ()

During the Occupation of Bajor, several Bajorans served as Cardassian collaborators, including Secretary Kubus Oak and Basso. () These collaborators either served the Cardassians directly, or provided the Cardassians with information on the Bajoran Resistance. 

Kevin Uxbridge was suspected of being a collaborator after the whole Rana IV colony was destroyed by the Husnock and only the Uxbridges' house was spared. ()

The homeworld of the Mizarian species, Mizar II, was conquered six times in three centuries due to the species never resisting their conquerors. When Esoqq, Kova Tholl and Jean-Luc Picard were captured together in an alien cell, Esoqq suspected that Tholl might be a collaborator with their abductors. When he indirectly suggested this idea, Tholl asked outright if he was accusing him of collaborating with their abductors and he replied that collaboration was what his species did best. Later, when identifying each member of the group's roles in the "laboratory maze" that their captors had structured, Picard described Tholl as the collaborator who would defer to whoever has control. ()

In 2365, a Bajoran chemist named Vaatrik, who lived on Terok Nor during the Occupation, served as a direct link between Gul Dukat and at least eight Bajoran sympathizers (i.e. Ches'sarro Seeto). Vaatrik would be executed by Kira Nerys. ()

In 2370, listing Quark's faults and why she despised him, Kira included collaborating with the Cardassians. ()

During the Dominion occupation of Deep Space 9, Kira initially worked alongside the Dominion in running the station in the belief that overt resistance would provide Dukat with the pretext to crack down on the station's Bajoran population. However, after Vedek Yassim killed herself on the Promenade in protest of the Dominion, Kira realized that, by making excuses for not fighting the Dominion, she had unknowingly become a collaborator. She and Odo thus began a resistance movement on the station. ()

Bajoran "comfort women" were also often accused of being collaborators. ()

In his war against the Dominion's occupation of Cardassia, Damar initially refused to attack any Cardassian guards, but ex-resistance fighter Kira countered that they were collaborators, and that the Dominion would place a Cardassian garrison at every critical facility once they realized that he wouldn't attack his own people. ()

In the Q Continuum, collaborating with the enemy was punishable by death. ()

List of known collaborators

Bajorans during Cardassian Occupation 
 Basso
 Ches'sarro Seeto
 Kira Meru
 Kubus Oak
 Opaka
 Vaatrik

Cardassians during Dominion War 
 Dukat
 Damar (former; later defected to Federation and rebelled against the Dominion)
 Broca
 Revok

External link 
 

de:Kollaborateur
Slang
Illegal occupations