Tormentor is the Catastrophic Quaken that lives in Dark Deep. Initially thought to be very hostile, he was discovered by Fishlegs Ingerman to just have been lonely and scared. Fishlegs was able to calm Tormentor down and help him make friends with the local Gronkles .
He made his debut in "Quake, Rattle and Roll".
As shown in "Quake, Rattle and Roll", Tormentor lived a lonely life in his cave on Dark Deep. He managed to take over the island, and drove all the Gronckles who were native to Dark Deep, to Dragon's Edge.
Hiccup and Fishlegs discovered the fearsome dragon and were forced to retreat back to the Edge. Back on the Edge, Fishlegs began to train with Snotlout to fight Tormentor and chase him away from Dark Deep.
During the final confrontation, Meatlug defended Fishlegs from Tormentor, putting the two Boulder Class dragons in a stare-down. Meatlug was able to see that Tormentor meant no real harm, but was actually acting out of self defense. Once Meatlug showed him kindness, Tormentor was accepted by the Dark Deep Gronckles and began living in peace with them. After this, he appears to have a small crush on Meatlug, though it is unknown if she returns his affections.
Thanks to the help of Meatlug, Tormentor had become very friendly to the Gronckles as he was willing to share his home with them to make Dark Deep a more peaceful island. He even showed forgiveness by breaking large boulders to feed his new friends.
Tormentor looks like any other Catastrophic Quaken. He has a grayish-silverish color on his scales, he has a Gronckle-like shape, and has a mouth with a bottom part that can separate in two. Tormentor is also shown to have orange-yellowish eyes as well. He contains many spikes on his head, with many on the top and on his chin, as well as a few small spikes on both of his wings.