Sestro

In the mirror universe, Sestro was an Iyaaran, a race of shapeshifters.

In the 2340s, Sestro impersonated $𝜇$. While impersonating Picard, Sestro was captured by the rebels aboard the $𝜇$. Sestro was then imprisoned because the crew of the Lakul did not trust Picard. However, Sestro was able to escape and beamed down to the planet the Lakul was orbiting in order to save the Lakul's away team from a $𝜇$ attack. In the rescue, Sestro was injured. Later, Sestro revealed that his people wished to undermine the Klingon-Cardassian Alliance, hence his deception. (SS undefined (The Traitor))