Closest Living Relatives: Hippopotamuses
We really hope this isn't some sort of hipporgy.
Well, that first assumption was semi-right, but we were way off the mark on that "huge lazy fatass" part. Just don't tell them that to their faces.
According to recent evidence, whales and hippos probably share the same great-great-great- (ad infinitum) grandpappy that lived about 50 million years ago. This ancestor split into two groups: the cetaceans and the anthracotheres. Believe it or not, whales and dolphins used to walk on land and were semi-aquatic, like crocodiles and otters. Here's a bad drawing of an Ambulocetus, an early whale ancestor: