The Gronckle is a dragon first featured in How to Train Your Dragon (Book 1), and is mentioned throughout the Book Series.
The Gronckle is described as the "plug ugly" of the dragon world. They are rather rotund, and can easily get too overweight to fly. They are also prone to dragon acne, perhaps accounting for their pimply hides. Gronckles also have huge sharp teeth.
- "Wartihog and Dogsbreath got into a loudly whispered fight over a Gronckle, a heavily-armored brute with fangs like kitchen knives sticking out in such numbers that it couldn't keep its mouth shut."
- ―How to Train Your Dragon (Book 1)
Gronckles can also grow rather large for a Hunting dragon. The Thin Prefect's Gronckle is stated to be two meters high (roughly 6.5 feet) and is able to pick up two boys in its mouth simultaneously. He also sports a horned ruff around his neck, something not seen in images of Gronckles.
Gronckles have extremely tough, armored skin with many sharp spikes. They also have a mace-like tail and dagger-sharp teeth. Though known not to be the brightest of dragon species, Gronckles are able to speak Dragonese.
Gronckles rate a "5" Disobedience score, and are therefore trainable. They are prized for their natural weaponry and skill in battle. Typically Gronckles are trained for battle or as hunting dragons. They have shown through the books to be rather loyal to their humans, and fought along side them in the Dragon Rebellion.
Gronckles were one of the original species to be mentioned at the beginning of the book, as the Hairy Hooligan novices entered the Dragon Nursery to grab a dragon to train. Individual Gronckles are then mentioned throughout the book.
Two individual Gronckles appear in Book 3 - the Thin Prefect's Gronckle and a Gronckle powering a Roman Hot Air Balloon. The latter is kept captive in a cage, while the former's status is dubious. The Thin Prefect's Gronckle takes orders from Thin Prefect, but also is un chained and uncaged and appears to be protective of him.
Gronckles are mentioned in this reference book.
- The Gronckle in the Hero's Guide to Deadly Dragons on the Official How to Train Your Dragon Books Website.