The Persian Kings didn't really "own" large swaths of the Empire since the Satraps had a great deal of autonomy.
"Wealthiest person of all time" is an interesting question.
Has to be either one of the Achaemenid Emperors or Alexander, right? The Persians controlled the Nile, Indus, Tigris, Euphrates, Oxus, the Levant, Anatolia.