Re: "when Sauron was mortal "
"back when Sauron was mortal"
"Isn't Sauron one of the Maiar? If so he was never mortal."
"You're thinking of his former boss, Morgoth."
Neither are, or were, mortal - both were "Ainur", the next level down from Eru Ilúvatar (the only "real" god in Tolkien's universe). The more powerful ones were called Valar, the lesser were called Maiar.
Sauron did actually "die" physically at least three times though...