The Seadragonus Giganticus Maximus, or just Sea-Dragon for short, is a dragon species in the books. These preposterously huge fire-breathing dragons are the size of a mountain, and are very dangerous; they kill for sport.

Seadragonus Giganticus Maximus are known to possess powers of telepathy and limited ability to see the future. They can breathe fire continuously for at least an entire night, which is powerful enough to dramatically alter landscapes. One Sea-Dragon, Wodensfang, has demonstrated possession of retractable teeth.

The promise of a Seadragonus Giganticus Maximus is considered to be unbreakable, although in practice there is nothing to ensure it.

Official Description

"Seadragonus Giganticus Maximus emerge from the egg as small as nanodragons. Over thousands of years they grow larger and larger until they are many times bigger than the big blue whale, as vast as mountains, as huge as islands."
The Incomplete Book of Dragons


Physical Appearance

This dragon is the largest (perhaps also the rarest) of all known dragon species; so large, in fact, that it has frequently been described as "blotting out the moon" when in full flight. Informally referred to as the 'king of dragons', these dragons are nigh-invincible and virtually invulnerable, possessing an immense amount of raw strength and power. Seadragonus Giganticus Maximus are blue, green, or purple, and usually covered in marine corals, anemones, and shells. However as it is discovered in How to Betray a Dragon's Hero, the size of these dragons change in line with their age. They start off extremely small, grow to an impossibly huge size, and sometimes shrink down to the earlier extremely small size (it is unknown why the similarly aged Green Death and Wodensfang were so differently sized -.possibly dietary differences control it).

As per How to Fight a Dragon's Fury, a full grown Seadragonus Giganticus Maximus have many extraordinary physical features and powers including, but not limited to, eyes at the back of the head, an unparalleled arsenal of fire-breathing abilities including fire blasts that explode on impact (vaporizing massive objects) and eyes that literally catch fire and flame. It is also suggested that dragons of this type may also have abilities unique to the individual specimen; not always replicated in their kin (for instance, the dragon Furious has demonstrated the ability to emit lightening bolts from his eyes). These dragons have also demonstrated strong (albeit limited) precognitive abilities; seeing through the barrier of time into the past and the future to perceive events that have not yet come to pass. They can telepathically communicate with other sea dragons, and their eyes have hypnotic qualities. Most sea dragons can also speak fluently in Norse, the Viking language.


The Green Death/Merciless

Main article: Green Death

A dragon that might be Merciless as shown on the cover of How to Train Your Dragon. Note that the Viking helmet in his talons is completely disproportionate if it is him.

The Green Death (or formerly known as Merciless) is the most well-known Seadragonus Giganticus Maximus. It claims, in the book, that it is an artist by eating other dragons, and is very proud of its size. In his youth, Merciless was the leader of the Dragon Rebellion, until Hiccup Horrendous Haddock I, using the Dragon Jewel, made him leave the Archipelago and never return, or else his fate--to be killed by a boy named Hiccup--would come to pass. A thousand years later, he returns to the Archipelago and is killed by the cunning of Hiccup the Third.

The Purple Death/Horror

Main article: Purple Death (Books)

The Purple Death (also called The Purple Horror) is one of three Seadragonus Giganticus Maximus to appear in the first book of the How to Train Your Dragon book series. It is said to be larger than the Green Death, but is eventually killed by it. Thuggory the Meathead is the first to notice the Purple Death after a terrible storm washes it up on the Isle of Berk. The Hooligans try to destroy both it and the Green Death by making them attack each other, which, despite the Purple Death being supposedly larger, resulted in the Green Death killing it.


Main article: Furious

A possible picture of the Dragon Furious from the UK cover of Book 8. However, Furious is said to be green in Book 8, and blue in Book 9, never red.


The Dragon Furious's hand roughly to scale from the US cover of Book 8. Note that its green color is a result of plant life growing on it.

Furious was Hiccup the Second's dragon, sometimes referred to as his "brother". After Hiccup was killed, he was captured and used by the Berserks as an executioner, and was turned bitter and evil over the years. He currently leads the Dragon Rebellion, whose goal is to exterminate the human race (Hiccup Horrendous Haddock III in particular).

The Wodensfang

Main article: Wodensfang

The Wodensfang


Possible art of the Wodensfang on the cover of the UK version of Book 9. However, the Wodensfang is not guarding Hiccup's sword, he is guarding the Crown, and he is brown, not blue.

It is revealed in How to Betray a Dragon's Hero that the Wodensfang is a Seadragonus Giganticus Maximus. He was the dragon of Hiccup Horrendous Haddock I. He stole the Dragon Jewel and gave it to Hiccup I, stopping the first dragon rebellion. When Hiccup III came around, he gave Hiccup III the Crown of the Wilderwest in the Fire Pit. Later, he makes a deal with the Dragon Furious that he will betray whoever becomes King of the Wilderwest to the Rebellion.


Main article: Toothless (Books)
Tribe toothless3

A baby Toothless from the books.

In How to Betray a Dragon's Hero, it is revealed that the Toothless from the books is also a Seadragonus Giganticus Maximus by the Wodensfang. He is Hiccup Horrendous Haddock III's dragon, a tiny, stuttering, toothless Common-or-Garden--so everyone thought. In time, Toothless will grow to the size of a mountain, possibly gain teeth, and then shrink again in his old age. He is the "Best Thing" of the King's Lost Things, according to himself.