There are multiple origins, definition and meanings for the Slavic name Oleg:
1. East Slavic (Russian Олег) popular name, derived from the word легко [lehko] means - "easy, easily".
2. Comes from the Scandinavian (Danish, Swedish and Norwegian) name Helgi meaning - "holy".
3. Indo-European name etymology - "Owl", comes from Sanskrit (उलूक) [ulūka], Germanic Eule, etc.