3. Frankenstein (1931)
The film that set the bar for the "mad scientist" archetype as well as the undead as a monster. While Frankenstein's creature itself isn't a zombie in the traditional sense it certainly influenced all the monster movies that came after it while Dr. Frankenstein was the first major character to show the psychotic nature of madness in film. Frankenstein also set up the legacy of all of the classic Hammer Productions horror films like The Wolfman, The Mummy, Dracula and many more. Dr. Frankenstein's influence can be seen in every sci-fi movie character who tries to cheat God and use science outside of its intended purpose to create a monster. Frankenstein showed that curiosity can be the most destructive thing in life if used for the wrong reasons which is a very common theme in almost every horror movie whether it's in a small way like a slasher character going in the room you know they shouldn't be going in, or it's more profound, like the crew of the Nostromo secretly being sent to pick up a facehugger in Alien.