About seven years ago, I suggested to the moderators we do something like the google doodles, specifically for Halloween that year. I was told it had been done occasionally before, but then several other moderators really ran with the idea.
I know Bear did several mooses...I don't know who did the code that automagically replaces it on certain holidays. But it was a team effort by a lot of folk to implement it - none of the work was done by me.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors