Knut the polar bear
Knut was arguably the most famous polar bear on Earth during his short life, which began on Dec. 5, 2006, and abruptly ended on March 19, 2011. He had been rejected by his mother shortly after birth, and was instead hand-reared at the Berlin Zoo by keeper Thomas Doerflein. While there, Knut became an international celebrity, reportedly earning millions for the zoo in merchandising and admissions. He even appeared on the cover of Vanity Fair in 2007.
A postmortem CAT scan concluded that Knut suffered an epileptic seizure, possibly due to encephelitis (although the cause of death was drowning, since he collapsed into his pool during the seizure). The zoo plans to build a monument, but its idea of stuffing Knut's body for display has been met with outrage by some fans.