pyromaniac; arsonist
Refers to a person with a compulsive urge to set fires. Often used in news reports and psychological contexts.
The police arrested the pyromaniac.
その連続火災は放火魔の仕業とみられている。
The series of fires is believed to be the work of an arsonist.
Compound of 放火 (ほうか, 'arson') and 魔 (ま, 'demon' or 'mania'), literally 'arson demon/maniac'.