Sion Radamantys Galaviz Medina is a Mexican chess grandmaster, born in 2005 in the state of Sinaloa and now based in Merida, Yucatan. He won the Alejandro Preve Castro Memorial in 2022 - finishing ahead of his own brother, Atlas Adomaitas - and took gold at the CONADE National Games in 2024.

His defining result came on board one for Mexico at the 45th Chess Olympiad in Budapest, where he scored 8.5/11 and earned a Grandmaster norm. He qualified for the 2025 Chess World Cup, and the title was completed in that period.