Author Beatrix Potter was born on July 28, 1866. Her books, mainly (entirely?) for children, featured such charecters as Peter Rabbit, Jemima Puddle-Duck, and Mrs. Tiggy-Winkle.
Beatrix Potter on LibraryThing.
Beatrix Potter on Wikipedia.
Update (3:50 PM): Who2's Editorial blog has a post featuring the graphic Google has on their homepage today. (That graphic is how I found out about the anniversary.)