Happy 500th birthday to you, John Calvin.
Except that your real name is Jean Cauvin.
The Presbyterian Church’s Calvin Jubilee has the explanation:
He was born Jean Cauvin, a Frenchman from Noyon. He was classically educated and wrote in the learned language of the day, Latin. The practice of the time was to use a Latinate form for the author’s name, so his Latin works were attributed to Johannes Calvinus. When these Latin works were then translated into English, the Latin name was Anglicized, leaving us with John Calvin.