Refers to someone who is mentally deranged or an extreme enthusiast. The 'fanatic' sense is often used in compounds like 釣り狂者 (fishing fanatic).
He is a fishing fanatic and is always at the sea on weekends.
The insane person was admitted to the hospital.
Compound of 狂 (kyō, 'insane, crazy') and 者 (sha, 'person'). The derivation is straightforward.