In all cities of this state that now have, or may hereafter attain, a population of five hundred thousand inhabitants or over, there shall be, and is hereby established, within and for said cities, a board of police, to consist of four commissioners, as provided in sections 84.040 to 84.080, together with the mayor of said cities for the time being, or whosoever may be officially acting in that capacity, and said board shall appoint one of its members as president, and one member who shall act as vice president during the absence of the president; and such president or vice president shall be the executive officer of the board and shall act for it when the board is not in session.
§ 84.020, RSMo