Could it be Sebastian Castellio ?
Professor Selderhuis biography: John Calvin, a Pilgrim's Life
on pages 140-142 tells the case of Castellio, who left Geneva
after several disagreements with Calvin and the City Council.
Castellio became a strong opponent of Calvin, and spent his
life opposing and distorting Calvin's teachings and decisions,
particularly the role of Calvin on the Servetus case.
This site is a detracting site based on Castelio's claims and writings against
Calvin:
Table of Contents: THE RIGHT TO HERESY or How JOHN CALVIN Killed A Conscience