Great Protector is a female Eruptodon, a Boulder Class dragon species. Great Protector lived inside a volcano on Caldera Cay and prevented said volcano from erupting, for which it is worshiped by the Defenders of the Wing. However, Great Protector was captured by the Dragon Hunters when Queen Mala was interrogating Hiccup Horrendous Haddock III and the rest of the Dragon Riders.
Becoming the "Great Protector"
Great Protector lived on the island, Caldera Cay. At some unknown time, Great Protector became the guardian of the human tribe that inhabited Caldera Cay, the Defenders of the Wing. She protected the Defenders of the Wing by preventing the volcano on the island form erupting, which would destroy their village.
One day, in the episode "Defenders of the Wing, Part 1", after being led by a supposed truce with the Dragon Hunters, the Dragon Riders arrived on Caldera Cay. When they got there, the riders saw a village, but were kidnapped by the Defenders of the Wing. The Defenders of the Wing believed the riders to be Dragon Hunter spies, but eventually Hiccup was able to convince their queen, Mala of the truth. However, the truce was all a ruse by Viggo Grimborn to lead the riders to Caldera Cay for use as a distraction, while they themselves went into the volcano and knocked out the Great Protector with Dragon Root arrows and kidnapped it. When Mala and Hiccup noticed that the volcano had excess lava spilling out, they walked to it and discovered the ordeal.