The office of the magister equitum (ME) (‘Master of the Cavalry’) was an office assigned to the dictator , and was never an independent office. Like the original designation of the dictator as magister populi (Master of the Infantry) (Cic. Rep. 1,40,63; Varro Ling. 5,82), it contains the word magister (root mag- = ‘head, leader’) and an indication of the original function as cavalry leader ( equites ).
The ME was appointed by the dictator as deputy (Liv. 8,32,1-8) for the period of his dictatorship. Appointment by a consul (Cass. Dio 42,21) or by …