main man
noun /ˌmeɪn ˈmæn/
  /ˌmeɪn ˈmæn/
 [singular] (informal)- a man who is important to you because he is a trusted friend or employee; the most important man in a situation
- Of course I trust you—you’re my main man!
 - The manager said I was going to be his main man in midfield.
 - He was chosen to replace Jordan as the main man at the sportswear firm.