maniac

Etymology

From mania + -ac. Borrowed from French maniaque, from Late Latin maniacus, from Ancient Greek μανιακός (maniakós), adjectival form of μανία (manía, “madness”). Doublet of manic.

noun

1. An insane person, especially one who suffers from a mania.
   She was driving like a maniac.
2. A fanatic, a person with an obsession.
   He's a manga maniac.