Lewis & Short

2. Rex, rēgis, m., a surname in the gens Marcia, e. g. Q. Marcius Rex, consul A. U. C. 686, Sall. C. 30, 3: Q. (Marcius) Rex, brotherin-law of Clodius, Cic. Att. 1, 16, 10 (in a lusus verbb. with rex, a tyrant, despot); cf. Hor. S. 1, 7, 35: P. Marcius Rex, Liv. 43, 1 al.; cf. Suet. Caes. 6.