Where does the name 'Aiden' come from?

It originated in Ireland. In Old Irish it was Áedán; in modern Irish, Aodhán, a diminutive of Áed (modern Aodh) which means 'fire'. The modern Irish pronunciation sounds like 'ae-aun' or 'ee-aun' as the 'dh' is silent.

Spellings in English are Aidan and Aiden.