nasilnik

1. (physical or psychological violence) violent person; abuser
   Policija je uhapsila nasilnika koji je tukao ženu. — The police arrested the abuser who had been beating his wife.
2. (at school, among peers) bully
   Moj sin se boji jednog nasilnika iz razreda. — My son is afraid of a bully in his class.

Unlike Russian «насильник», the word does not usually mean rapist; that is silovatelj.