This is Teddy Roosevelt's hunting trophy. Theodore Roosevelt is responsible for creating the US National Parks. He was an outdoorsman and hunter. This trophy represents a time before our knowledge of the impact of hunting endangered species. I have no doubt that had he known the impact of his actions at the time, he would have opposed the hunting of endangered species. His trophy still stands as a reminder of who our president was as well as a means to educate others on the importance of preservation.
More about the elephant (Henry) can be found at Smithsonian National Museum of Natural History
Update
This elephant is actually Henry. It's not the elephant Roosevelt shot. Roosevelt led an expedition to bring animals to the museum. The elephant he shot is actually one of eight in Akeley Hall of African Mammals