I call him Father Christmas because I'm English. My husband, who is American, calls him Santa Claus.

Santa Claus/Santa/Santy is what he's always been called in Ireland (and Scotland from what I read) so it isn't just an American thing. That was the heated debate I was reading about the topic. people got very ummm "passionate" about the subject

I've always called him Santa. In Portuguese we call him "Pai Natal" which literally translates to "Father Christmas".