Lovok

Lovok was a male Romulan who lived in the 24th century. He was a member of the Tal Shiar and held the rank of colonel in the 2370s.

In 2371, Lovok was imitated by a Changeling after the Founders learned of Enabran Tain's plan for the Cardassian Obsidian Order and the Tal Shiar to join together to annihilate their species by destroying their homeworld. The Founders hoped that by luring the Romulans and Cardassians into a trap, it would leave only the Federation and the Klingons for the Dominion to deal with, with plans already in motion. After the Jem'Hadar attacked the fleet, "Lovok" revealed that he was a Changeling to Odo and Elim Garak and helped them to escape, due to the Changeling belief of not harming another. Lovok pleaded with Odo to return with him to the Great Link, although Odo refused. 

''In an alternate timeline in which the Cardassians did not leave Bajor and Changelings infiltrated every major power, Lovok was in charge of providing the military information on the Klingons when the Romulans were engaged in a war with them. Lovok would later be killed by a Changeling impersonating Koval, allowing the Founders to completely infiltrate the Tal Shiar.