right-hand man; trusted assistant; second-in-command
Refers to a person who supports a leader or manager from a close, behind-the-scenes position, like a chief of staff or deputy. The literal meaning is 'wife role', but it is used for both men and women in a professional context.
As the president's right-hand man, he supports the company's practical operations.
She serves as the department head's trusted assistant, handling everything from scheduling to negotiations.