Office 365 has 5 different management roles. And one of the roles is that of the Global Administrator. This role is given the highest possible privileges. They can set up accounts manage billing, services and monitor health too.
More than one person can be a global administrator. So only a person who is a global admin can add another person in his/her role.
They are the only admins who can create other admin roles. As I had mentioned previously that Office 365 has 5 Admin roles, only the Global admin has got the privilege to create other admin roles.