I thought I knew about every museum cat of any reputation (even the bad ones), but I never knew about THE museum cat - Mike, of the British Museum (1909-1929). He was dropped off as a tiny kitten at the doorstep of Sir E. Wallis Budge, the Museum's Keeper of Egyptian Antiquities, by Black Jack, the feline incumbent of the institution. It's a poor student that doesn't excel his master, and Mike became the most famed kitty associate of this great museum. But to read all about him, you should go right now to this excellent page at Purr-n-Fur UK.
Meanwhile, here is a link to the Museum's stunning Mexican cat-head ring (Mixtec, circa 12th-16th c) and a sweet-faced Egyptian cat mummy coffin.