Why does the Pope change his name ?
Why the name change? While there doesn’t appear to be a written rule barring Popes from using their real names, it’s been de facto Papal law since the mid-16th century to switch. Currently, it’s the very first question the new Pope is asked after being elected, while still ensconcedin the Sistine Chapel.
The practice of name-switching appears to have started in 533, when a Pope with a pagan name–Mercurius–was elected. Having deemed that unsuitable for obvious reasons, he switched to John II. Between his and Marcellus’s reign, some Popes kept their given names, and some didn’t.
I was always under the impression, it was because Jesus Changed Peters name from Simon??? I'm pretty sure they taught that in Catholic school when I was in grade school.