The Tax Commissioner shall be appointed by the Governor, subject to confirmation by the General Assembly, if in session when such appointment is made, and, if not in session, then at its next succeeding session. He shall hold office at the pleasure of the Governor for a term coincident with that of each governor making the appointment, or until his successor shall be appointed and qualified. Vacancies shall be filled in the same manner as original appointments are made. No person shall be appointed Tax Commissioner unless he is a person of proved executive ability and knowledge of taxation. He shall devote his full time to his duties and shall receive such compensation for his services as provided by law.