Alexander m. Ancient Greek ἀλέξω 'I defend' + Ancient Greek ἀνδρός, gen. of Ancient Greek ἀνήρ 'man'.
The name of a 2nd C pope and saint, a 3rd C Roman emperor, five 3rd C saints, three 4th C saints, a 5th C saint, a 10th C Byzantine emperor, an 11th C pope, two 12th C popes, a 12th C king of Scotland, a 13th C pope, two 13th C kings of Scotland, a 13th C prince of Novgorod and Kiev and saint, a 15th C antipope, a 15th C saint, two 15th C kings of Georgia, a 15th c prince of Wallachia, a 15th C grand duke of Luthania, a 15th-16th C pope, and a 16th C prince of Moldavia. Wycliffite Bible (1395): Alisaundir
The popularity of this name was reinforced by various medieval Romances about Alexander the Great, one of the nine worthies.