Spawned from fanart, people like to group the different incarnations created from the history of the character in a selfcest relationship and work off a dynamic from there.
Hiccup from the first movie. Hiccup Horrendous Haddock III, son of Stoick the Vast, was the worst viking his village has ever seen. Wanting to prove himself, he invents a bola-catapult that shoots down a Night Fury. Unable to kill the Night Fury, he frees it and later befriends the misfit dragon, naming him "Toothless" for his retractable teeth. He learns new things about dragons from working with Toothless, using his new skills to become the most popular viking in the village, and realizes that everything his tribe ever knew about dragons was wrong. After fellow dragon-trainee Astrid discovers Toothless, the three discover dragon's nest, and learns about a massive dragon that forces dragons to feed it at the cost of their lives. After nearly losing everything, Hiccup and Toothless saves the tribe from the dragon at the cost of his leg and peace between vikings and dragons is achieved in the process.
Hiccup from the second movie. Five years after the events of the first movie, Hiccup has become the recurring hero of Berk and the fabled "Dragon Conquerer" and "Dragon Master." In his new flight suit and flaming sword "Inferno", Hiccup learns of a madman by the name of Drago Bludvist who intends of conquering the world with an army of dragons. Reuniting with his long lost mother, Hiccup faces against Drago (losing his father in the process), defeats the mad warrior and his Bewilderbeast, and takes on his rightful place as "Chief of Berk."
Hiccup from the original book series. Hiccup learns how to be a hero the hard way, accompanied by his best friends Fishlegs (who is even less Viking-y than Hiccup, with asthma, glasses, eczema and an allergy to reptiles), Camicazi (the daughter of the Bog-Burglar Chief, nearly two years younger and a head shorter than Hiccup, and can escape from nearly anywhere and knows it), and, of course, his disobedient dragon, Toothless.
Note: Please add only ones that are part of the RotBTD fandom