Just after conqueting Constantinople, Mehemet the conqueror received from Pope Pius XY (I do not remember the numeral, name was Enea Silvio Piccolomini) a proposal on the lines of: let's convert yourself to christ and I will crown you "Emperor of the Christians" (after all, he had conquered the "true" Roman Empire, so he could claim the title of Caesar by right of conquest).
The intriguing fact is that the pope was himself an almost-atheist politician and in his letter he highlined the many similarities between the two religions, and was proposing a de-facto blending.
I think his actual words were:
"Everyone knows of your rightousness, of your piety, of your god-fearing.
In order to become christian you just need to add some water".
On the other hand, after his refusal, the pope tried to organize a crusade against him