Sidekicks are the partners and/or companions of a hero.

Many of them are usually the deuteragonist/tritagonists/tetartagonists working for the protagonist, though it can go other ways. Some may be anthropomorphic animal sidekicks. For the most part they are a supporter of the hero in the story. The most famous example of a sidekick in fiction is Robin, the Boy Wonder, the sidekick of the superhero Batman.

Usually, when the sidekick gets bored of their job or feels like their partner doesn't treat them well, they go off to start their own life as a hero. Their villainous counterparts are the Right-Hands, who are accomplices of a villain and Henchmen, Pawns, and Minions, who frequently work for villains.