This 1920 German silent film is widely considered the first true horror movie. While a few earlier films dealt with supernatural, ominous themes, "The Cabinet of Dr. Caligari" established the foundations of the genre [source: Ebert]. Tension rises and releases, an ominous villain stalks the scenes and the setting feels mysterious and unsettling. Another German horror film, "Nosferatu," followed two years later and also casts a long shadow across the horror genre [source: Feaster].
"The Cabinet of Dr. Caligari" influenced more than just the horror genre. It also played a major role in the German Expressionist movement, which sought to depict dark emotions like madness and confusion by using exaggerated plots and unrealistic settings. This worked very well for horror movies -- "Cabinet" incorporates bizarrely shaped buildings and walls at odd angles to create viewer unease. These influences show up in every era of horror filmmaking, from the 1920s sci-fi horror of "Metropolis" to the modern stylized fright of Tim Burton.
Watch "The Cabinet of Dr. Caligari" for free at Archive.org.