Green Death

The Green Death is a colossal evil dragon and the main antagonist of the novel How To Train Your Dragon, and its animated movie adaptation. In the movie though, it was renamed the Red Death.

Role in the books
In the first book, the Green Death arrives on Long Beach with a smaller Seadragonus Giganticus Maximus (which it eats later on). Hiccup is sent to meet with it and asks if it comes in peace or war as he is the only one who can speak Dragonese.

When Hiccup says his name the dragon shivers subconsciously it seems however that Hiccup did not notice it nor did the Green Death itself. The dragon says he comes in peace but that he's still going to eat them all regardless. The Green Death and Hiccup discuss Singing Suppers, but during the conversation the Green Death moves in to eat Hiccup.

Just as this happens the Green Death yawns, and decides he's too tired to eat Hiccup right now, stating that he should come back in a few hours to be eaten. Hiccup then leaves and tells the tribe that the Green Death, while coming in peace, will still eat them. With the help of the other Hooligan and Meathead boys and their dragons, Hiccup creates a plan to kill the Green Death with the help of a second Seadragonus Giganticus Maximus, the Purple Death, which they trick into helping them.

In the following battle the Purple Death is killed but the Green Death is fatally wounded. In anger, the Green Death swallows Hiccup whole. Fortunately, Hiccup avoids being digested by grabbing and holding on to a Roman spear stuck in the dragon's throat. While inside the Green Death, Hiccup discovers the fire holes (a dragon's source of fire) and blocks them with his helmet. Due to this, the Green Death blows up when it tries to burn Stoick, Hiccup and Toothless. Its death makes Hiccup a hero in the eyes of his tribe.

In How to Steal a Dragon's Sword, the Green Death was known as Merciless, the leader of the Dragon Rebellion in Hiccup Horrendous Haddock the First's time. Merciless saw in the future that he was to be killed by a human named Hiccup. He sent Wodensfang to kill Hiccup, but was instead betrayed by Wodensfang when Wodensfang discovers the good in Hiccup's heart. With the Dragon Jewel, Hiccup ordered Merciless to disband the Rebellion and become a loner.

In flim
In the movie adaptation, the Seadragonus Giganticus Maximus is renamed the Red Death. It serves primarily as the movie's indirect main villain. Initially seen dwelling in the volcanic interior of the Dragons Nest, the Red Death acts as a parasite, sustaining itself off of all the livestock its 'dragon servants' bring it as a meal.

It eats anything that contributes little to nothing, as seen with a sole Gronckle who donates a single fish, and anything that gets in its way will also become eaten, as seen when a Hideous Zippleback got in its way when it was attempting to escape as the red death was trying to eat Toothless, Hiccup, and Astrid. The dragon almost takes the oppurtunity to eat up Toothless when it spots that he has contributed nothing and has humans on his back. Hiccup, Astrid and Toothless barely manage to escape.

In the movie its gender is debatable. Astrid refers to it as a "Queen" but she is speaking metaphorically comparing the dragon mound to a bee hive. However Hiccup calls him a he when he say to Toothless,"Well he can fly!" So the Red Death is most likely a male dragon since Hiccup says he is and his counterpart in the books is also male.

The Red Death isn't seen afterward until the climactic battle between it and the Vikings. Stoick arrives with the rest of the village on the island housing the Nest and succeeds in scaring off the dragons that serve the Red Death. Enraged at the Vikings, the Red Death soon breaks through the mountainside to destroy them. The teenage Vikings soon arrive on their own dragons to fight off the beast. While the other Viking teens distract the Red Death, Hiccup nearly drowns after trying to save and unchain Toothless on one of the boats which the Red Death had set fire to. Luckily, both of them are saved by Stoick and Hiccup, along with Toothless, takes off to confront the Red Death.

After circling the island once, Toothless begins to anger the Red Death by launching a fireball at the monster's side. The enraged dragon then pursues Toothless and Hiccup into the skies where Hiccup decides to use the heavily clouded sky as a cover. Toothless then attacks the Red Death in the clouds with a barrage of fireballs aimed toward its thin wings. The Red Death angrily sets the entire sky, as well as Toothless' makeshift tail, on fire. After seeing this, Hiccup and Toothless decide to finish the dragon once and for all by skydiving towards the island with the Red Death hot on their heels. With the beast just above them, Toothless launches a fireball directly into the flammable gases within the Red Death's mouth. The gases ignite violently inside the Red Death as it discovers that it cannot pull out of its skydive with its wings in tatters. The Red Death crashes into the island and combusts in a bright, fiery explosion.

The victory comes with a cost. As the dragon explodes, Toothless collides with it's huge tail and sees Hiccup fall off his back and into the fire. Even though the Night Fury is able to save his human friend's life, Hiccup's left leg is burned and mauled beyond repair. He eventually gains a prosthetic as a replacement for his limb. Despite his grief over the loss of his left leg, Hiccup is finally relieved that the enslaved dragons are now free from the Red Death's control and that they are starting to live with the Vikings in peace, ending the war between them for good.