The dragons known by the Hairy Hooligan Tribe are grouped into one of eight classes based on their characteristics and abilities. The eight known classes are Stoker, Boulder, Fear, Sharp, Tidal, Tracker and Strike. In the exclusive short, Book of Dragons and in episode 20 of Dragons: Riders of Berk, the idea to categorize dragons into individual classes was started by Gobber's great-great-great grandfather named Bork the Bold.
Stoker Class dragons are hotheaded fire breathers, and most of them are capable of setting themselves on fire. They include the Monstrous Nightmare, the Terrible Terror, the Typhoomerang, the Fireworm, the Red Death, and the Hobblegrunt.
The known dragons in the Stoker class are Hookfang, Torch, Fanghook, Gruff, the Monstrous Nightmare that Astrid trained, the Fireworm Queen, and the six Terrors trained by the teens (only four were named: Sharpshot, Iggy, Butt and Head).
Boulder Class dragons are tough and associated with the earth. They can eat rocks, and despite that their wings are smaller compared to their entire body, they are able to fly as fast and as high as most other dragons can. The Gronckle, the Whispering Death, the Screaming Death, the Hotburple and the Snafflefang are members of this class.
Fear Class dragons are stealthy, sneaky, and often have multiple heads. Instead of fire, they breathe gases with different effects. The former dragons of this class are the Hideous Zippleback and the Snaptrapper.
In HTTYD 2, Fear class seems to no longer exist due to the fact that Vikings are now living peacefully with dragons instead of fearing them. Instead, the Fear Class symbol is used for the new Tracker class.
Tidal Class dragons live in and near the ocean, and unlike most dragons, they don't have fire breaths as their ranged attacks. The dragons in this class are generally larger in size than most of others. The Scauldron, the Thunderdrum, the Seashocker, and the Bewilderbeast are classed here.
Mystery Class dragons have little known about them. The original members of this Class are the Changewing, the Boneknapper and the Smothering Smokebreath. Later on the Hideous Zippleback, the Flightmare and the Snaptrapper were moved to this classification.
The Red Death used to be a Mystery Class dragon, until it was moved to the Stoker Class.
Strike Class dragons are overall extremely powerful. They have blazing speed, pin-point accuracy, vice-like jaw strength, powerful attacks and extreme intelligence. They are also the most difficult to train, but the most loyal once training has been accomplished. The Skrill and the Night Fury are the dragons in this class, and both dragons are emblems of the Berserker Tribe and Berk respectively.
The Tracker Class is a new class found in the How To Train Your Dragon 2 website, The symbol of this class replaces the Fear Class symbol, despite the Hideous Zippleback not being in this Class. The dragons in this class have highly acute sense of smell to track and find things. The dragons in this class are the Rumblehorn, and the Deadly Nadder.
The Unknown Class is a temporary fan-made Class for dragons that don't have a class. These dragons may possibly be sorted into different classes in the future. The current members are the Grapple Grounder, and few other How To Train Your Dragon 2 dragons.
- 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.
- It is possible that the Mystery Class is a sort of "temporary" class where dragons are put when little is known about them, and then when they are more thoroughly understood they are moved to another class. For instance, the Night Fury could have been a Mystery Class dragon before the events of the first movie, and then moved to the Strike Class once it was studied and trained by Hiccup.
- On the How To Train Your Dragon website, Stormfly is shown to be in the Sharp Class and the Tracker class, this is due to the Fear Class being changed to Tracker Class. Stormfly is also a member of the Sharp Class according to the short, the Book of Dragons.
- On the How To Train Your Dragon website, Barf And Belch are shown to be in the Mystery Class, this is due to them changing class, since Fear Class is irrelevant as of March 14 2014.
- The Unknown Class is actully a fan-made Class made for dragons whose Class is still unknown. Seeing how the Grapple Grounder was the first dragon whose Class still hasn't been revealed, it is the symbol of said Class.
- It may be possible that the Grapple Grounder is a Strike Class or a Stoker Class Dragon.
- With six known species in each class, the Stoker Class and the Mystery are the largest Dragon Classes.
- With two known species in each class, the Strike Class and Tracker Class are the smallest Dragon Classes.
- It has been shown that the dragons are occasionaly reclassified. All Fear Class dragons were moved into the Mystery Class, and the Red Death was moved from the Mystery Class to the Stoker Class. The Flightmare was a Strike Class dragon, untill it was moved to the Mystery Class. The Hobblegrunt used to be a Boulder Class dragon, but was reclassified as a Stoker Class dragon by the Dragonpedia. The Snafflefang used to be a Stoker Class dragon, but was reclassified as a Boulder Class dragon.