Not all zombies are flesh-eating ghouls. Some are simply slaves under the influence of powerful drugs (see The Serpent and the Rainbow, which I'll be talking about later this month). Others are slaves under the influence of something else altogether.
In 1920, director Robert Weine made what is considered by many to be the first horror movie, ever. The Cabinet of Dr. Caligari tells the story of Francis (Freidrich Feher) and his friend Alan (Hans Heinrich v. Twardowski), who attend the carnival in Hostenwall. They visit a booth where Dr. Caligari (Werner Klaus) opens a cabinet to reveal the "somnambulist" Cesare (Conrad Veidt). Caligari claims Cesare can answer any question posed to him. Unwisely, Alan asks when he will die and Cesare says "Before dawn." Sure enough, the prophecy comes true.
Francis and his fiancee Jane (Lil Dagover) investigate, discovering that Caligari is using hypnotism (a relatively new concept in 1920) to force Cesare to kill. When they get too close, Caligari has Cesare kidnap Jane with the intention of killing her but Cesare's last vestiges of humanity won't allow him to do his master's bidding and he takes off with her. The townspeople of Hostenwall give pursuit and after abandoning Jane, Cesare dies of exhaustion.
It turns out (in film's first 'twist' ending ever - spoiler alert!), that Francis, Jane and Cesare are all actually inmates in an asylum run by a man obsessed with with an 18th Century monk named Caligari and the story was all in Francis' head.
Now I can hear some of you hardcore film buffs whining that Thomas Edison's 1910 version of Frankenstein was the first horror movie. But Edison's movie (directed by J. Searle Dawley) is a clumsy, silly short that wouldn't scare a toddler. Weine's film combines atmosphere, weird sets and a complex original story to create a surreal psychological thriller featuring a 'zombie' more in keeping with the Voodoo concept along with a surprise at the end. Cesare is truly a frightening figure and Caligari is a prototypical villain, forcing an unwilling slave to do his evil bidding. There is a reason that people still talk about this movie 90 years after it was made. You can see the full 72 minute movie on YouTube here, but here's a taste of the atmospheric masterpiece:
If you've never seen The Cabinet of Dr. Caligari, I highly recommend you seek it out. It is truly essential for anyone who is seriously interested in not only horror movies, but film history in general. It continues to influence modern filmmakers such as Tim Burton and is one of the few films to rate 100% on Rotten Tomatoes. In 2006, director David Lee Fisher digitally inserted modern actors (and audible dialog) into Weine's film, with mixed results. Most critics hated it.