3 Undead Lessons From George Romero, Who Created the Modern ZombieThe filmmaker died on Sunday after an aggressive battle with lung cancer.

Slow, plodding hordes of flesh-eating walking dead are a regular and integral part of pop culture, but it wasn't that way until George A. Romero filmed and releasedNight of the Living Deadin 1968.

The New York-born filmmaker took what had been a voodoo myth -- the zombie -- and turned them into the "neighbors," because, as he said, "there's nothing scarier than the neighbors!"

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The film centers on Barbra, who along with her brother, are chased by zombies after visiting their father's grave. She manages to take shelter in a farmhouse, and is joined by Ben, a truck driver also seeking refuge. The characters then struggle to survive the night as the dead surround them. The claustrophobic, documentary like feel of the film still remainsscary to this day.

The film, made for about $114,000, went on to become a big hit, earning about $30 million at the box office.

Romero's debut feature film was also notable in that an African American man, Duane Jones, played the lead character. As Romero was driving to a meeting to pitch his movie, the Rev. Martin Luther King, Jr., was assassinated, andNight of the Living Deadtook on more of a racial statement.

Romero died on Sunday after "a brief but aggressive battle with lung cancer," his family said in a statement. He was 77.

Here are some key lessons from the career of Romero.

1. Don't rest on your first success.

Romero could have easily settled into his role as the zombie guy, but he always strived to take on new and different challenges. His next film,There's Always Vanilla,was a romantic comedy. Even after he returned to zombies, with 1978's pivotalDawn of the Dead,he took on a new tone and tact. That film, set in a shopping mall, was more of a satire on American consumerism.

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2. Know when it's time to move on.

Romero's final movie,Survival of the Dead,released in 2009. That year,Zombielandalso released and became the highest grossing zombie movie up until that point with a box office take of more than $100 million.

"That was the first one to turn the ... box office corner and you know, gosh, all of a sudden, you can't make a little zombie film anymore," he told NPR in 2014. "I figured well, if I do it as a comic book I can let my imagination go bananas and I don't have to worry about shooting it."

He also dabbled in video games, a medium whichhe creditsfor the popularity of zombies.

3. Give people a reason to come back.

Blood and guts will only get you so far. There's a reason Romero was so beloved among directors: his movies had a timeless depth.

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"What George did is give us, in [zombies], a dark mirror in which we can reflect socially; to learn what in them remain us and what it is to be human," director Guillermo del Toro toldRolling Stone. "George was an iconoclast, an untamed mind and a liberal thinker who used horror to illuminate the darkness around us."

Edgar Wright, director ofShaun of the Dead,which was heavily inspired by Romero,wrote: "Even if he was pigeonholed somewhat in the genre realm, one of the reasons that his work resonates still is because of fierce intelligence and humour behind it. His zombie films alone are the work of a major satirist, being highly vivid socio-political metaphors and sometimes better records of the years in which they were made than countless serious dramas."