There is a trope character I like to call “Professor Exposition.”
We often see Professor Exposition appear in horror movies. This is the character who explains to the leads (and by extension the audience) what is doing the haunting, perhaps a bit of backstory, and how to potentially stop it.
He’s called Professor Exposition because this is a character whose primary story function is to deliver a pure blast of exposition, straight no chaser. Typically, exposition is a necessary evil, with an emphasis on evil, because exposition is boring, and it’s very hard to write and act this stuff in a way that’s organic. But Professor Exposition provides one of the rare examples of exposition that can play as organic simply because consulting with him is something we would buy doing ourselves under the same situations.
Sometimes, Professor Exposition shows up in act one. For example, it’s a commonly used trope to give our protagonist a lecture to attend, at which Professor Exposition is speaking. The lecture’s function is to a) show that our protagonist is a smarty-pants; b) blast the audience with some exposition that will pay off later in the story.
Note this isn’t always a lecture, one excellent example being the unctuous Purcell in the original (1992) version of CANDYMAN. Ironically, this film also gives us a lecture hall scene, but the lecture’s pertinence is more tangential.
We also see a model that saves Professor Exposition for act two. This version seems to more often occur in ghost/demon-type movies, for instance Vincent D’Onofrio’s character in SINISTER, or J.K. Simmons in DARK SKIES. The leads suffer through two acts of being haunted, and in trying to figure out what’s going on they turn to Professor Exposition for an explanation.
Note that Professor Exposition fits this trope because it’s his main function. There are examples of characters offering an exposition dump, though their main function is not to provide exposition. For instance, in the FRIDAY THE 13TH movies, we’ll often get a scene in which a character gives everyone the lowdown on Jason Voorhees and Camp Blood. This person isn’t Professor Exposition. We might call this take on exposition the “Telling of the Legend,” or more specifically “The Campfire Story.”
Professor Exposition is often a supporting protagonist, and frequently only exists for a scene or two. However, there are films in which Professor Exposition is our protagonist. For example, at different times both Father Karras and Father Merrin act as Professor Exposition. The CONJURING FILMS are from the POV of the Warrens; two Professors of Exposition who go around explaining what’s going on to people who are being haunted. The same could be said of Lin Shaye’s character Elise Rainier in the INSIDIOUS franchise.
The overall point being: Professor Exposition is a part of the screenwriting toolbox. Exposition is one of the tougher parts of the script to nail, and the good Professor offers a tried-and-true strategy to deal with it in a way that goes down smooth.