A sidekick is defined by the American Heritage dictionary as "a close companion or comrade." The sidekick is used in the heroic fiction as a plot device to forward the story. Usual ways that writers use the sidekick are to either have the hero explain what is going on to the sidekick (and therefore, the reader) or by having the sidekick placed in peril therefore requiring the hero to rescue him.

Comic book fiction brought the sidekick to its own with the introduction of such characters as Robin, Speedy, Kid Flash, Aqualad, and Bucky. These characters were used to give young readers some one to identify with in the stories. Not all sidekicks were younger versions of their hero counterparts, however. Kato, the Green Hornet's companion and driver, and Tonto, the Lone Ranger's Indian companion, both broke this mold.