The loneliest whale. It's a whale that communicates at the wrong frequency so other whales can't hear them.

https://en.wikipedia.org/wiki/52-hertz_whale

Nobody is quite sure what species it is, what's wrong with it, or anything. There's theories that it's the last member of an extinct species which would be very cool, but more likely it's a known species, possibly a blue whale, with a disability of some type.