Trajok's species were a race of humanoids, likely from the Alpha or Beta Quadrant. Their faces had three sets of thorned ridges, two on each side of their foreheads and one in the middle.
Contact between the Federation and this species occurred prior to 2370. (DS9: "Playing God")
Given Trajok's appearance, it is possible that he was actually a full-blooded Ktarian, as evidenced by the subtler features seen on the half-Ktarian Naomi Wildman of USS Voyager.