In the Books
The blubber keeps it warm in cold climates.The vikings use this to their advantage, using the dragons' blubber to keep themselves warm in intertribal swimming races. It looks similar to a Gronckle.
In the Movies
Although it has not been confirmed that it exists in the movie franchise, a very similar dragon was shown in How to Train Your Dragon 2 . It appeared next to Gothi and Gobber at the end of the movie. It has a blue color and is so fat that its legs do not touch the ground.