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 Poetica 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 Les Misérables, the song "Master of the House" relieves much of the sadness shown before it in the musical.
In the Mortal Kombat series, notably in Mortal Kombat (2011 video game), Johnny Cage is an actor who believed the Mortal Kombat tournament was a movie set, and often tried 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.
In Gone With the Wind, after Scarlett has a fight with Ashley, she throws a dish at the wall. Rhett Butler sits up from his lying position on the couch, where, unknown to Scarlett, he was eavesdropping. He looks at the shattered dish and asks if the war has started.
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.
Current hit TV series Pawn Stars has a store employee, Austin "Chumlee" Russell, who is affectionately called "our village idiot." He is a childlike bumbler who creates messes and can get away with making insulting but true remarks that would get many people fired. Chumlee is somewhat of an idiot savant, ignorant of store antiques but expert in toys and tennis shoes. Like a teenager, he sneaks off to the back storage room to bowl and swing a samurai sword, which damages the items. Spin-off TV show American Restoration also has a simpleton (folklore) employee Brettly, who often acts without thinking. He pays full price for a damaged car. He can break the things he is supposed to fix. The simplest chores are said to be "Brettly-proof."

DEFINITIONS
A humorous or farcical interlude in a serious literary work or drama, especially a tragedy, intended to relieve the dramatic tension or heighten the emotional impact by means of contrast.
A humorous scene, incident, character, or bit of dialogue occurring after some serious or tragic moment. Comic relief is deliberately designed to relieve emotional intensity and simultaneously heighten and highlight the seriousness or tragedy of the action. Macbeth contains Shakespeare's most famous example of comic relief in the form of a drunken porter.