His main goal in the film is to marry Belle, simply because she's the most beautiful girl in town. When he is first rejected by her, he becomes disgraced but cheers up after the villagers sing a song about him. When Maurice comes in talking about Belle being imprisioned by a Beast, Gaston plans to have him put into an asylum unless Belle agreed to marry him.
When Belle is able to prove the Beast was real, Gaston realizes Belle was in love with the Beast and organizes the villagers to kill the Beast. Though the villagers are defeated by the enchanted furniture and tools, Gaston makes it to the Beast and shoots him with an arrow. The Beast lets Gaston pummel him, having lost the will to live, but once Belle arrives and asks Gaston to stop hurting the Beast, the Beast finally fights back and eventually grabs Gaston by the throat and prepares to toss Gaston off the castle. Gaston begs for his life and the Beast lets him go. Gaston sees the Beast hold Belle's hand and stroke her hair and then stabs the Beast in the back. Gaston then loses his balance and falls to his death.