While not immediately hostile to you, conversing with them will reveal their antagonistic nature and choosing certain dialogue options (particularly on the topic of Talos worship) can turn them hostile toward you. Thalmor Justiciars can be found traveling the roads, sometimes with a Nord prisoner in tow, and engaging any Stormcloaks they see in combat. By 4E 201, the Thalmor has established a significant presence in northwest Skyrim, including an embassy in the mountains overlooking Solitude, a fort known as Northwatch Keep (used as a covert detainment center for their political prisoners), and an unused building within Solitude which was set aside for the Thalmor by the Empire. A militarist regime founded on beliefs of racial supremacy, the Thalmor seek to advance their power and influence across Tamriel with the specific intent of establishing the racial superiority of Mer over Man, ' one century at a time'.
The Thalmor is the combined government of the third Aldmeri Dominion and according to Ondolemar represents an alliance between Altmer and Bosmer regents.
