What does it take to create a monster?

Aileen Wuornos must have asked herself that as she stood in front of her dingy bathroom mirror — naked, dirty, spotted in blood — an image she didn’t recognize staring back at her.

“Monster,” based on the true story of a Florida prostitute-turned-serial killer, shows the deterioration of an already battered woman who enacts revenge on a world that has let her down. Charlize Theron’s shocking performance as Aileen becomes the focal point in a most disturbing way. This murderer becomes the eye of a never-ending storm that surrounds her. Whether you like it or not, Theron’s Aileen asks for — and receives — your complete attention.

In early 1990, Aileen Wuornos was convicted of murdering seven men, claiming abuse and self-defense in all cases. Her indifference was questioned at the time, and Wuornos’ motivations are still questioned — most notably by British filmmaker Nick Broomfield in two documentaries: 1992’s “Aileen: The Selling of a Serial Killer” and this year’s “Aileen: Life and Death of a Serial Killer,” opening at the Gene Siskel Film Center this month.