Mister Big
noun [ S ] humorous uk/ˌmɪs.tə ˈbɪɡ/ us/ˌmɪs.tɚ ˈbɪɡ/
大人物，举足轻重的人物
the most important person in a place or organization
Paul is Mister Big in our department, so it's important to make a good impression on him. 保罗是我们部门的大人物，给他留下好印象至关重要。