What does Diego mean?
A Spanish name of genuinely disputed origin. Traditionally explained as a short form of Santiago (Sant-Yago, 'Saint James', from Hebrew Jacob), but many scholars now derive it instead from the Latin Didacus — itself possibly from the Greek didache 'teaching'. The two theories remain unresolved, so any single 'meaning' should be treated with caution.
What does Thiago mean?
A form of Tiago, drawn from Santiago ('Sant Iago', Saint James) by resegmenting San-Tiago. The 'Th' spelling is Portuguese-influenced and hugely popular across Latin America. Ultimately traces to the Hebrew Ya'aqov (Jacob), via James.