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, Tracker, Sharp, Tidal, Mystery, 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. This class contains dragons that can set themselves on fire, as well as most of the smaller species. When a Stoker Class dragon lost their fire, it is a sign to show that they are going to die, although their flames can be reignited by a Fireworm Queen's venom or by eating their Flame Gel combs. The dragon species included are:
- Monstrous Nightmare
- Terrible Terror
- Red Death
- Night Terror
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
- Grapple Grounder
- Catastrophic Quaken
The Tracker Class is a new class that was discovered in Race to the Edge. The symbol of this class reuses the Fear Class symbol, despite the Hideous Zippleback not being in this Class. Tracker Class dragons have highly acute sense of smell or taste to track down 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
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:
- Sand Wraith
- Tide Glider
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
- Hideous Zippleback
- Sword Stealer
- Death Song
Strike Class dragons have blazing speed, pin-point accuracy, vice-like jaw strength, powerful attacks, explosive firepower and extreme intelligence. 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 Strike Class' flag color is purple.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. This can also happen if a dragon is so new that we don't have much information on it or its class. Finally, this can happen if an unknown dragon only makes a cameo in the media it appears in. Therefore, the dragon itself could not be identified, much less could its class be identified. The currently unclassified dragons are the three original dragons from the Arena Spectacular, the unknown dragons in How to Train Your Dragon 2, a known dragon from HTTYD 2, two unidentified dragons that appear in the Book of Dragons short, one currently unclassified alpha dragon from Rise of Berk, several concept art dragons from the first movie, and a currently unclassified new dragon who will appear in Race to the Edge. Many of these dragons are currently unclassified due to the lack of information on their species.
- Egg Biter
- Unknown Dragons
- Cavern Crasher
- Unidentified Dragon (Book of Dragons)
- Unidentified Dragon Two (Book of Dragons)
- Unknown Concept Art Dragons HTTYD
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. This class was removed and replaced with the Tracker class was most likely the fact that Vikings no longer fear dragons any more.
- Since the vikings didn't know what a Night Fury looked like until the taming of Toothless, the Strike Class should logically be symbolized by the Skrill, or another Strike Class dragon. 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. However, due to all of the Fear Class dragons being moved into the Mystery Class, this may no longer be true.
- 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 three known species, the Tracker Class is currently the smallest Dragon Class.
- With ten known species in each class, the Sharp Class and the Tidal Class are currently the largest Dragon Classes.
- It has been shown that the dragons are occasionally reclassified. All Fear Class dragons were moved into the Mystery Class. The Flightmare was a Strike Class dragon, until it was moved to the Mystery Class. The Red Death also used to be a Mystery Class dragon, until it was moved to the Stoker Class. The Snafflefang used to be a Stoker Class dragon, until it was moved to the Boulder Class. The Deadly Nadder was a Sharp Class dragon, until it was moved to the Tracker Class. The Hobblegrunt used to be a Boulder Class dragon, until it was moved to the Stoker Class.
- The Deadly Nadder, the Hideous Zippleback and the Grapple Grounder symbolize the Sharp Class, Tracker Class and the fanmade Unknown Class, despite no longer being in them.