I might be wrong but I vaguely remember from one of the OU courses that the role was originally written for a "star" castrato at the time (when it was a must to have castrati in leading roles in Italian operas). The music was also revised slightly when it was later performed by another castrato. But since castrati weren't fashionable in France, the music was again reworked for the Paris performance (also to suit the French taste e.g. adding ballet) Will dig out the OU books if I have time
Other operas I can think of: Handel's Tamerlano and Rinaldo, something Egitto by Mayerbeer. I think Mozart's Idomeneo was originally a castrato role as well but later revised as tenor.