“When there's no more room in hell, the dead will walk the earth.”
Source: Dawn of the Dead
George Andrew Romero was an American filmmaker, writer, and editor. He is best known for his series of gruesome and satirical horror films about an imagined zombie apocalypse, beginning with Night of the Living Dead . This film is often considered a progenitor of the fictional zombie of modern culture. Other films in the series include Dawn of the Dead and Day of the Dead . Aside from this series, his works include The Crazies , Martin , Creepshow , Monkey Shines , The Dark Half and Bruiser . He also created and executive-produced the 1983–88 television series Tales from the Darkside.
Romero is often noted as an influential pioneer of the horror film genre and has been called an "icon" and the "Father of the Zombie Film." Wikipedia

“When there's no more room in hell, the dead will walk the earth.”
Source: Dawn of the Dead
As quoted in "10 Questions for George Romero", TIME, (June 07, 2010) http://content.time.com/time/magazine/article/0,9171,1992390,00.html
As quoted in George A. Romero: "Who Says Zombies Eat Brains?", Vanity Fair (27 May 2010) http://www.vanityfair.com/hollywood/2010/05/george-romero