Every limited company organization is headed by a board of directors, and the chairman of this board of director is designated as chairman of the company. In this way theoretically the chairman of the company is the highest ranking officer of any company.
Directors, and the chairman of the board of directors of a company exercise a general policy making and supervisory role in the management of the company. They are not required to get involved in day to management or or executive role. That function is performed by the executive management and operational people. The highest ranking officer among these is designated by different names in different companies. One such popular designation is CEO (Chief Executive Officer). A CEO may be heading a complete company or just a division within company.
In some smaller companies the the Chairman of the company may also perform the function of the CEO.