The main role of the fairies in William Shakespeare's "A Midsummer Night's Dream" is to introduce the magic into the story that both causes problems and helps to bring about a happy ending. They give a surreal character to the play and contrast some of the more coarse characters in the story. They also help to add the humor a comedy needs to be successful.
Puck, the main fairy character and arguably the main character of the play, brings a huge comical element to the story. His magic gets him and the human characters of the play into a great deal of trouble. His mistake in giving the wrong character love potion brings heartache and upheaval into the love affairs of the humans, but he manages, later through his magic, to right his wrongs and bring the intended couples back together. Sometimes, however, he just uses his magic for his own purposes, as he does when he turns Bottom's head into the head of a donkey. The antics of the fairy king, Oberon, and his queen, Titania, also provide the audience with fun. The part where Titania falls in love with the sometimes insufferable Bottom gives the opportunity for some human-fairy interaction. No story exists here without the presence of the fairies and the magic they provide.