What we wind up with is a race of four-armed reptilian creatures that have a very different silhouette and profile than other alien races. The Tzenkethi employ modular and adaptive technology, but they tend to favor the same strategies time and again, and the designers stress that your first encounters against them should prove the most difficult. So they’re going to be a different sort of foe on all levels, not just in the sense of looking different. Pretty good for a species we only heard mentioned in the background by Captain Sisko.
The Tzenkethi are coming to Star Trek Online, which should make any franchise lore nerd at least moderately happy. No television series has ever featured the Tzenkethi in the flesh, but they were discussed extensively in Deep Space Nine; we knew that they fought a war with the Federation and weren’t necessarily friendly. So the designers of the game just had to create a design for these aliens to make them a credible threat while also differentiating them from all of the other threats players have faced in the game over the years.
Source: Official Site