Demons

On the Berlin subway, university student Cheryl gets off at her stop in the deserted subway station and is pursued by a mysterious, masked man. Rather than attacking her, the man offers her tickets to a free screening at the Metropol, an isolated and recently renovated local cinema. Cheryl talks her friend Kathy into going with her and they skip class to go see the film. At the crowded theater, they meet two preppy college boys, George and Ken, who take an immediate liking to the girls and help them get a can of cola out of the vending machine. The four sit together in the theater.
There are many people from all walks of life in the audience; a blind man and his guide daughter; an elderly married couple; a boyfriend and girlfriend; and a pimp named Tony along with his two prostitutes, who look at the theater's display props in the foyer. One of the prostitutes, Rosemary, scratches her face with a bizarre display mask before they go in to watch the film. The film is a violent, disturbing horror movie which features a look-alike of the mask from the lobby. It is about four teenagers who discover an old tomb and dig up the grave of a sixteenth-century fortune teller called Nostradamus. When the teenagers dig up Nostradamus's coffin they find no body, just an old book and a mask identical to the strange mask in the foyer. When one of the characters puts the mask on he's scratched by it just like Rosemary was by its doppelganger. A moment later, he turns evil and slaughters his friends with a knife.
Rosemary feels ill and goes to the bathroom, where the scratch on her face bursts open, spewing out pus. She is soon transformed into a bloodthirsty, green-skinned, red-eyed, fanged demon like the one in the film. Rosemary attacks her friend, Carmen, who then rips through the screen and transforms into a demon in front of the rest of the cinema-goers. The group of uninfected people race to any exit they can find, only to find that they have all been bricked up making escape impossible. Although they attempt to barricade themselves in the balcony, many are attacked and infected by the demons. One of the demons escapes into the city when four punks break in to the building through a back entrance. The punks are soon transformed into demons as well.
In the cinema, only George and Cheryl remain uninfected. Using a display motorcycle and sword props from the foyer, they ride through the auditorium, slicing down many demons. George kills nearly all of them when suddenly, a helicopter crashes through the roof. George and Cheryl use an emergency grappling hook and winch to climb to the roof, where they are attacked by the mysterious man from the subway. They are able to kill him by impaling his head on an exposed bit of rebar. The two climb down to the street and discover that the demonic infection has spread throughout Berlin. They are then chased by a horde of demons before being picked up by a jeep of well-armed survivors (a father and his two young children) and they make their escape. As they drive out of the city to safety, Cheryl transforms into a demon. She is shot and killed by one of the other passengers and falls out on to the road, leaving George as the cinema's only survivor.

Question: Who is Pursuing Cheryl?
Answer: A mysterious, masked man