Lewis & Short

regnātor, ōris, m. [regno], a ruler, sovereign (poet.): deūm regnator, Naev. ap. Fest. s. v. quianam, p. 257, 28 Müll.; Verg. A. 4, 269: deorum, Plaut. Am. prol. 45; cf.: summi Olympi, Verg. A. 7, 558; 10, 437: regnator omnium deus, Tac. G. 39: corniger Hesperidum fluvius regnator aquarum, Verg. A. 8, 77; Col. 10, 200: Asiae (Priamus), Verg. A. 2, 557 Wagn.: Neptunus regnator marum, Naev. ap. Prisc. p. 770 P.; cf. of the same: freti, Sen. Hippol. 945: lyricae cohortis (Pindarus), Stat. S. 4, 7, 5: agelli, i. e. owner, Mart. 10, 61, 3.
With dat.: occiduis regnator montibus Atlas, Val. Fl. 2, 621: Illyricis regnator aquis, i. e. the Danube, Aus. Epigr. 3.
Absol.: in Siciliā, ubi rex Agathocles regnator fuit, Plaut. Men. 2, 3, 58; Mart. 11, 6, 2.