Is Light a villain ou a hero?

He's the main character, making him the protagonist. But he is the villain. L, Light's antagonist, who tries to keep Light from his goal, is the good guy. Being the antagonist isn't evil, it just someone who tries to prevent the main character (Light) from reaching their goals. So, Light is the villain

*ahem* I like to see him as plus misguided, but...

He is the god of the new world he does what is necessary to vanquish evil. praise thy name Lite