ringleader; main culprit
Refers to the person primarily responsible for a crime, plot, or wrongdoing.
警察は事件の元凶を逮捕した。
The police arrested the ringleader of the incident.
Used for the fundamental cause of a problem, disaster, or undesirable situation.
環境破壊の元凶は人間の活動だ。
The main cause of environmental destruction is human activity.
He is said to be the root of all evil.
The factory wastewater became the main cause of the river pollution.
The police tracked down the mastermind behind the incident.