Slavic ban "leader"

Can anyone on the list tell me about current theories regarding the
origin of the word ban, "leader/governor" in various Slavic languages
(as well as in Romanian and Hungarian). I have heard two theories so
far - one, that it is an Iranian loan (allegedly cognate with Farsi
ban "prince/lord" - but is that a genuine word?), or that it is
rather an Altaic loan, cognate with Turkish bayan "very rich man".

Any help would be greatly appreciated.
- Chris Gwinn