Morris the Explainer
Morris the Explainer is a fictional character (by whatever name) whose job it is to explain the plot or parts of a plot to other characters and the audience. This storytelling cliché is also known by the names Sam the Explainer and Jake the Explainer.
The origin of this narrative device is probably found in early mystery stories, where the end often consists of the police or a private investigator confronting a room full of suspects and explaining who committed the crime, why and how it was done. This easy-way-out technique was given a funny send-up in A Shot in the Dark by Blake Edwards and William Peter Blatty, where Inspector Clouseau (Peter Sellers) delivers a perfect parody of crude mystery solutions in film. A famous example for Morris the Explainer from a serious context is the Architect in the film The Matrix Reloaded by Laurence and Andrew Wachowski. A mentor can also be misused as a Morris the Explainer.
However, an explainer doesn't have to occur only at the end of a narrative, and a similar technique found throughout a modern film narrative is the expositioning character, who is used by writers to explain certain elements of the story along the way. Expositioning can surface as the so-called technobabble, e.g. in the television series Star Trek: Voyager, or as an over-pychologized storytelling, where the writer prefers to let the characters talk about their emotions and motivations rather than letting them act according to their needs and intentions.