Zombie films may be the most common subgenre of horror films. The dead, resurrected and with an insatiable thirst for human flesh, can serve as an allegory for a variety of social problems, or they can be a simple, easily identifiable threat to characters in rudimentary horror films.

The best zombie films do not just throw the raging undead at hapless humans. Some of the most influential films in the history of horror have been zombie ones, and zombies have branched out into comedy and romance as the genre has grown. Here are seven important zombie films that show how much filmmakers can accomplish within this basic framework.

Without George A. Romero's landmark 1968 film, the zombie genre as we know it would not exist. Romero did not attempt to define the entire horror genre, and Night of the Living Dead takes place primarily in a secluded farmhouse, where the characters hide from the undead insurgency.

From the eerie and disturbing opening in a graveyard to the gut-wrenching ending, Romero never lets up, leaving the audience standing with the characters as they face chaotic and unimaginable situations. Whether you've seen dozens of zombie movies or have seen this particular film multiple times, Night of the Living Dead is a visceral terror.

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Elements of the zombie genre are so ingrained in pop culture that even audiences who have never seen a zombie movie are prime targets for parody. Director Edgar Wright takes advantage of this in this pitch-perfect horror comedy, poking fun at familiar zombie movie clichés while telling an effective story about fighting the undead.

The main character, played by Simon Pegg, is initially unaware of the zombie outbreak and must work with his best friend Ed (Nick Frost) to come up with a haphazard plan to avoid the zombie attack and rescue his loved ones. Wright blends clever movie references and self-aware humor with a deep understanding of the genre he is playing with, making "Shaun of the Dead" both a heartwarming comedy and a horror film with a genuine sense of danger.

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This South Korean box office smash has an irresistible hook, featuring passengers trapped on a commuter train that is rapidly filling up with zombies. Due to the nature of the zombie infection, everyone on the train is a potential killer, and as the train continues its journey, the ratio of zombies to humans only increases. Director Yong Sang-ho builds up the tension as the protagonists gradually realize how dangerous they are in the situation.

Director Yong also staged impressive set pieces in the limited space of the train, sticking to a single location to achieve blockbuster-style action. While there are somewhat cheesy character arcs for some of the passengers, the emotional storytelling keeps the film grounded as the zombie attacks become more intense and brutal. It is no wonder that this ambitious yet accessible film eventually launched a franchise.

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Can a zombie movie be a romance? That question is surprisingly answered in the affirmative in this film adaptation of a popular young adult novel. It is also about much more than just the love story between zombie-obsessed R (Nicholas Hoult) and human resistance fighter Julie (Teresa Palmer). It is about fostering understanding between opposing factions, even if one of those factions is literally undead.

R and Julie's romance begins with a kidnapping, but as it blossoms into something deeper, Holt and Palmer give their characters an emotional connection that combines passion and empathy. The villain here is not the largely passive zombie, but Julie's militaristic human father (John Malkovich), who must embrace a new path of peaceful coexistence.

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HBO's "The Last of Us" popularized the idea of zombies controlled by an insidious fungus, but this film, based on M.R. Carey's novel, got there before the TV series. Both explore the idea of a real-life fungus that can control the behavior of ants, mutating into a form that can control humans. The film takes a more hopeful approach, set in a post-apocalyptic world where humanity has a better understanding of how zombies function.

The title character (Senia Nanua) is a young girl held captive by a military group studying the evolution of zombies, particularly the evolution of children who speak and reason like Nanua's Melanie. Melanie remains on the run with her teacher (Gemma Arterton) as they work toward a future shared by zombies and humans, charting a new phase in the existence of both.

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