Svetoslav m. Slavic svet, sviat, from Proto-Slavic *světъ, from Proto-Indo-European *ḱweytos 'bright, shine' + Slavic sława, slava 'glory, fame'.
The name of a 10th C king of Croatia, a 10th C grand prince of Kiev, an 11th C grand prince of Kiev, a 12th C grand prince of Kiev, a 12th C prince of Novgorod, and a 13th C prince of Novgorod.