Comic relief

Comic relief is the inclusion of a humorous character, scene, or witty dialogue in an otherwise serious work, often to relieve tension.

Definition
Comic relief usually means a releasing of emotional or other tension resulting from a comic episode interposed in the midst of serious or tragic elements in a drama. Comic relief often takes the form of a bumbling, wisecracking sidekick of the hero or villain in a work of fiction. A sidekick used for comic relief will usually comment on the absurdity of the hero's situation and make comments that would be inappropriate for a character who is to be taken seriously. Other characters may use comic relief as a means to irritate others or keep themselves confident.

Use
Sometimes comic relief characters will appear in fiction that is comic. This generally occurs when the work enters a Dramatic moment, but the character continues to be comical regardless. Greek tragedy does not allow any comic relief. Even the Elizabethan critic Sidney following Horace’s Ars Poetic pleaded for the exclusion of comic elements  from a tragic  drama. But in the Renaissance England Marlowe among the University Wits introduced comic relief through the presentation of crude scenes in Doctor Faustus following the native tradition of Interlude which was usually introduced between two tragic plays. In fact, in the classical tradition the mingling of the tragic and the comic was not allowed.

Examples
William Shakespeare deviated from the classical tradition and used comic relief in Hamlet, Macbeth, Othello, The Merchant of Venice and Romeo and Juliet. The Porter scene in Macbeth, the grave-digger scene in Hamlet and the gulling of Roderigo provide immense comic relief. The mockery of the fool in King Lear may also be regarded as a comic relief.

In popular culture, the character of C-3PO, featured in all six Star Wars films, is also considered to be used as comic relief. He is often found criticizing the desperate situation the other characters find themselves in, or being rescued from predicaments by his counterpart R2-D2.

In the Mortal Kombat series, notably in the 2011 reboot game, Johnny Cage is often described as a comic relief, in which he is depicted as an actor who believes the Mortal Kombat tournament is a movie set, and often tries to impress Sonya Blade. Rain is also a joke character, since his attire is purple, and his name came from the Prince song "Purple Rain".

Many of Akira Kurosawa's films had a comic relief character, most notably of which in The Seven Samurai, with Kikuchiyo the drunken warrior who claims to be 13 years old, despite the obvious fact that he's too tall and has too much facial hair to be of that age.

The Power Rangers television series franchise features Bulk and Skull. They are classmates to Angel Grove High School's secret identities of the Power Rangers and sometimes bullies while also sometimes serving as assisting secondary characters.