Information dealers who trade in secrets and are often seen as untrustworthy across the Alpha Quadrant.
The Yridians are a humanoid species with wrinkled, hairless heads who are known as dealers in information. They travel widely and sell secrets to whoever will pay, so other species treat them with suspicion.
The best known Yridian is Jaglom Shrek, played by James Cromwell, in the Next Generation episode Birthright. While the Enterprise-D is docked at Deep Space Nine, he approaches Worf and claims that Worf's father, Mogh, did not die at Khitomer but is being held in a secret Romulan prison camp. Worf at first doubts him, but he later pays Shrek and forces him to take him to the camp.
There Worf finds Klingons who had been captured at Khitomer and their children living in hiding, though his father is not among them. The episode shows the Yridian trade at work: a tip that was partly false still sent Worf into Romulan territory and changed the lives of the people he found there.