sponsor; promoter; impresario; organizer; organiser
イベントの主催者は参加者の安全に責任を持つ。
The organizer of an event is responsible for the safety of participants.
主催者に問い合わせたところ快く対応してもらった。
When I contacted the organizer, they were happy to help.
主催者側の手違いで開始時間が遅れた。
The start time was delayed due to a mistake on the organizer's side.