Gary Gygax, co-inventor of Dungeons and Dragons, published this note explaining why Christians (like him) shouldn't celebrate Christmas.

A note from Gary Gygax in the IFW Monthly of February 1969. A topical historical curiosity, yes, but what does it tell us about who Gary was back then? First of all, he strongly self-identified as a Christian, an important counterpoint to the fundamentalist backlash against his later fantasy-themed games. Gary approached Christianity as a system with rules, which he researched and explored through a strict historical lens. If his readings differed from mainstream conventions, he was never one to bow to popular opinion. Sometimes he took things too seriously, sacrificing fun for accuracy. He was never shy about sharing his ideas and defending his position in public, but respectfully acknowledges the existence of dissenting views. These are all qualities we see reflected in his subsequent career as a game designer.

Gary Gygax on Christmas and Christianity [Jon Peterson/Playing at the World]