The dragons known by the Hairy Hooligan Tribe are grouped into one of six classes based on their characteristics and abilities. The six classes are Stoker, Boulder, Sharp, Tidal, Tracker and Strike class. 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. However, it is possible to lose their fire, a sign that shows that the stoker dragon is about to die. This can be reignited by a Fireworm Queen's venom or by eating their Flame Gel combs. The dragon species included are:
The known dragons in the Stoker class are Hookfang, Torch, Fanghook, Gruff, the Monstrous Nightmare that Astrid trained, the Wild Fireworm Queen, the Red Death, Sharpshot, Iggy, Sneaky, Pain and 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 dragon species included are:
- Whispering Death
- Thunderpede (Rise of Berk)
- Groncicle (Rise of Berk)
- Grapple Grounder
The Tracker Class is a new class found in the How To Train Your Dragon 2 website. The symbol of this class reuses 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 dragon species included are:
Sharp Class dragons are vain and prideful, and they all possess sharp body parts. The dragons included are:
- Speed Stinger
- Hackatoo (Rise of Berk)
- Shivertooth (Rise of Berk)
Tidal Class dragons live in and near the ocean, and unlike most dragons, they don't use fire breaths as their ranged attacks, although very few can, they rarely do use them. The dragons in this class are generally larger in size than most of the others. Hiccup also said that a Tidal class dragon can't stay out of the water for a long time, but this is false for some of these aquatic dragons. The dragons included are:
- Shockjaw (Rise of Berk)
- Sand Wraith (Rise of Berk)
- Tide Glider (Rise of Berk)
- Desert Wraith
Mystery Class dragons have little known about them due to how stealthy and sneaky they are. All dragons in this class are generally feared more so than the other dragon classes. The dragon species included are:
- Smothering Smokebreath
- Sweet Death (Rise of Berk)
- Hideous Zippleback
- Sword Stealer (Rise of Berk)
Strike Class dragons have blazing speed, pin-point accuracy, vice-like jaw strength, powerful attacks and extreme intelligence. Strike class dragons utilize lightning in their ranged attacks, Skrills absorbs lightning and fires it; Night Furies breathe acetylene and oxygen shaped charges that form a type of plasma, which creates a mixture of fire and electricity. The dragons in this class are the rarest of all, are near close to extinction, and also the most difficult to train, but the most loyal once training has been accomplished. The dragons included are:
Some dragons have not yet been officially classified in any class. These dragons may possibly be sorted into different classes in the future. The reasons for this lack of information may vary, but usually it's associated with the dragon being created by a company other than dreamworks. The currently unclassified dragons are the Arena Spectacular original dragons: Stinger, Gobsucker, and Egg Biter dragons. Many of the new How To Train Your Dragon 2 dragons are currently unclassified due to the lack of their information.
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.
- 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 discovery and 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, the Deadly Nadder is shown to be in the Sharp Class and the Tracker class, this is due to the Fear Class being changed to Tracker Class. The Deadly Nadder 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.
- With two known species, the Tracker Class is currently the smallest Dragon Class.
- With nine known species, the Tidal Class is currently the largest Dragon Class.
- It has been shown that the dragons are occasionaly reclassified. All Fear Class dragons were moved into the Mystery Class. The Flightmare was a Strike Class dragon, untill it was moved to the Mystery Class. The Red Death also used to be a Mystery Class dragon, untill it was moved to the Stoker Class.
- The Deadly Nadder,Hideous Zippleback and Grapple Grounder symbolize the Sharp Class,Tracker Class and The fanmade Unkonwn Class, despite no longer being in them.