Sidekick
A sidekick is a stock character, a close companion who assists a partner in a superior position. Sancho Panza in Don Quixote, Dr. Watson in Sherlock Holmes, and Robin, Batman's companion, are some well-known sidekicks.
Origins
The origin of the term comes from pickpocket slang of the late 19th and early 20th century. The "kick" is the front side pocket of a pair of trousers, and was found to be the pocket safest from theft. Thus the "side-kick" became an inseparable companion. ([1] [2] [3])
Use in Fiction
In fiction, the term sidekick most commonly refers to assistants to heroes, usually in a crimefighting capacity. The sidekick has the literary function of playing against the hero, often contrasting in skill, asking the questions the reader would ask, or performing functions not suited to the hero.
Function of the Sidekick
Those functions may include comic relief. The comic sidekick was a common feature in westerns, where Fuzzy Knight, Al "Fuzzy" St. John, and Andy Devine had longer careers than some of the heroic singing cowboys for whom they took pratfalls. In science fiction a subtype of sidekick has been established - namely, the Alien sidekick.
Hero Sidekicks not only provide comic relief but can occasionaly be brave & or resourceful at times and rescue the hero from some dire doom: such as Streaky the Supercat of Krypto the Superdog or Festus Haggen of Gunsmoke's Matt Dillon.
Sidekicks also frequently serve as an emotional connection, especially when the hero is depicted as detached and distant, traits which would normally generate difficulty in making the hero likable. The sidekick is often the confidant who knows the main character better than anyone else and gives a convincing reason to like the hero. Although Sherlock Holmes was admittedly a difficult man to know, the friendship of Dr. Watson convinces the reader that Holmes is a good person.
Comparisons
A villain's supporters are normally called henchmen, minions, or lackeys, not sidekicks. While this is partially a convention in terminology, it also reflects that few villains are capable of bonds of friendship and loyalty, which are normal in the relationship between a hero and sidekick.