Leo Gabalas (Greek: Λέων Γαβαλᾶς) was a Byzantine Greek magnate, who in 1204, with the dissolution of the Byzantine Empire by the Fourth Crusade seized the island of Rhodes. There he established there a separate, sovereign principality, which extended over the nearby Aegean islands, claiming the titles of "Caesar" and "Lord of Rhodes and the Cyclades".
In 1226, the Nicaean emperor John III Vatatzes launched an expedition against him and defeated him, forcing him to acknowledge Nicaean suzerainty. Gabalas remained in control of Rhodes however, and soon began reasserting his independence. In 1233, a new Nicaean expedition against him under Andronikos Palaiologos failed. In the very next year Gabalas signed an alliance with Venice directed against Nicaea, and even provided support to the Venetians against the Nicaean-sponsored rebellion of the Greek inhabitants of Crete. Leo ruled Rhodes until his death in 1239/1240, when he was succeeded by his brother John Gabalas.