key person; keyman
Refers to an indispensable person in an organization or project, often a decision-maker or central figure.
彼はこのプロジェクトのキーマンだ。
He is the key person for this project.
キーマンが辞めてしまったので、計画が遅れている。
The plan is delayed because the key person quit.
He is the key person for this project.
He became the key person on the team.
We looked for the key person in order to move the negotiations forward.