The dragons known by the Hairy Hooligan Tribe are grouped into one of seven classes based on their characteristics and abilities. The seven classes are Stoker, Boulder, Fear, Sharp, Tidal, Mystery, and Strike. In the exclusive short, Book of Dragons, the idea to categorize dragons into individual classes was started by Gobber's great-great-great grandfather named Bork the Bold.

Stoker Class

Stoker Class dragons are hotheaded fire breathers. They include the Terrible Terror, the Monstrous Nightmare, the Typhoomerang, and the Fireworm.

Boulder Class

Boulder Class dragons are tough and associated with the earth. They can eat rocks. The Gronckle and the Whispering Death are members of this class.

Fear Class

Fear Class dragons are stealthy, sneaky, and often have multiple heads. The known dragons of this class are the Hideous Zippleback and the Snaptrapper.

Sharp Class

The dragons of the Sharp Class are vain and prideful. They also possess sharp body parts, such as spines. The Deadly Nadder and the Timberjack are grouped in this class.

Tidal Class

Tidal dragons live in and near the ocean. The Scauldron and the Thunder Drum are classed here.

Mystery Class

Dragons in this class have very little known about them. In this class are the Changewing, the Boneknapper, and the Smothering Smokebreath. Also, according to the How to Train your Dragon Live Spectacular's program book, the Red Death is a mystery class Dragon.

Strike Class

The Strike Class dragons are super fast, intelligent and have incredible vice-like jaw strength. The dragons of this class are the Skrill and the Night Fury.

Trivia

• The Grapple Grounder is not grouped in any of the classes mentioned above, nor does it have one of its own. Though it's been described as being rather similar in behavior to a Night Fury, as well as having very similar firepower, it could be a Strike Class dragon.
• Since the vikings didn't know what a Night Fury looked like until the taming of Toothless, the Strike Class should logically be symbolised by the Skrill. It is possible that the Strike class's symbol was changed by the Hooligans to have a new symbol after the taming of Toothless.