What is the difference between a ceo and a chief of staff?

ICYMI: A chief of staff works with and through the same team as the CEO: other members of the senior leadership team. A director of operations has his own team and direct reports (vice-presidents, directors, managers).
https://www.chiefofstaff.blog/what-is-the-difference-between-a-ceo-and-a-chief-of-staff