They are known as Google Doodlers, a mix of mostly twenty-something artists and engineers whose sole job it is is to create small works of art that we forget about when we wake up the next day.
http://www.technobuffalo.com/2013/03/08/google-doodles-team/
http://www.cbsnews.com/8301-505263_162-57573229/googles-doodler-team-how-artists-engineers-remake-internet-giants-logo/