Original: In eastern Spain, Jacobus became "Jacome" or "Jaime"; in Catalunya, it became Jaume, in western Iberia it became "Iago", from Hebrew Ya'akov, which when prefixed with "Sant" became "Santiago" in Portugal and Galicia; "Tiago" is also spelled "Diego", which is also the Spanish name of Saint Didacus of Alcalá.
Simplified: In eastern Spain, Jacobus became "Jacome" or "Jaime"; in Catalunya, it became Jaume, in western Spain it became "Iago", and Portugal and Galicia it was Tiago.