Characters are what allows the player to get access and to start a quest which in the end rewards you with , , , , and in some quests, , an item, or a Dragon Egg. In cases like Battle Events and Stable Missions, a character will also give you a tutorial on how does the minigame works.
They're scattered across the locations, some in multiple locations at once, except when a quest involves a character to be in a specific location.
There's a total of 26 character (not including your Viking) divided in 3 categories.
Movie Characters are character derived from both How To Train Your Dragon and How To Train Your Dragon 2 movies, and to an extent, from the TV Shows (Dragons: Riders of Berk, Dragons: Defenders of Berk and Dragons: Race to the Edge) as well.
Being derived from the movies and TV Shows, it's very likely that they will make references and mention an event from the movies or TV Shows in the middle of a quest, sometimes with a clip of said part of the respective episode or movie. Some of the quests like Mysteries of Gronckle Iron are directly based on an event from the TV Shows or movie.
While characters like Hiccup and Mulch have the same roles as they have in the movies/TV Shows, characters like The Alchemist, who's actually Heather, and Phlegma the Botanist, a character that had a very small screentime, have high roles and in case of The Alchemist, a complete different role from the TV Show. The game also tries to add additional information to the characters and can go as far as to break the canon universe's story.
Book Characters are characters derived from Cressida Cowell's How To Train Your Dragon book series.
Unlike the Movie Characters, the Book Characters do not make any reference to the books nor do they look similiar to the book appearance, in fact, by buying the correct clothing and Facial War Paint, you can customize your Viking to look exactly like them because they were made with the player's customization and body built. One of the major differences between the book characters in the book and in the game is how Speedifist is white as opposed to black in the book, its skin color got changed for unknown reasons.
These characters are rarely used as they only appear in 2-3 beginner quests.
Original Characters are characters that were made by the SoD team and are very often used in multiple quests, if not, quite forcebly added into the quests. The most used character, Skulder, is often forcebly added in expansions for the sake of the player having to save Skulder from any sort of trap or cage.
They often have a close relation to the player while simultaniously not trusting the others, to the point of fully trusting them and consider them as their friend.
These characters are often built with the intension of attempting at forcing their stories and relation with some characters into the canon universe and even going as far as break the canon universe's story and create a plot hole for the sake of developing the Original Characters' plot.