A reclusive humanoid species whose government runs deep-cover agents against the Orion Syndicate, one of whom Odo falls in love with in A Simple Investigation.
The Idanians feature in the Deep Space Nine episode A Simple Investigation. Idanians tend to keep to themselves, and their government maintains an intelligence service prepared to go to extreme lengths to place agents inside criminal organisations.
In 2373 Odo meets Arissa, a woman on the run from Draim, a boss in the Orion Syndicate for whom she has worked as a data thief. Odo protects her and the two become lovers, his first such relationship with a humanoid.
An Idanian agent then reveals that Arissa is one of their own. Her appearance was surgically changed and her real memories were removed and stored in a data crystal so that she could pass any test of loyalty. Once the memories are restored she is an Idanian with a husband at home, and she and Odo part.