A Delta Quadrant species who give off a substance that makes other species forget them soon after they leave, a trait that shaped Chakotay's ill-fated romance.
The Ramurans are a secretive Delta Quadrant people who naturally release a pheromone that causes members of other species to forget them shortly after contact ends. Their society keeps itself isolated, and members who leave are hunted down by trackers and brought home, with their memories of the outside world wiped.
In the episode Unforgettable, a Ramuran tracker named Kellin came aboard Voyager seeking asylum and told Chakotay that they had fallen in love during an earlier visit he no longer remembered. They began a new relationship, but another tracker caught her and erased her memories, and Chakotay was left to lose his own recollection of her as well.