In common sense, a Dovahkiin (meaning Dragonborn in ancient dragon language) is a rare individual that was born with dragon blood but with the body of a mortal. They can naturally speak the ancient and powerful tongue of the dragons. However, when referring to the [last] Dovahkiin, the individual we are speaking about is the main protagonist and playable character of The Elder Scrolls V: Skyrim as well as it's expansions Dawnguard and Dragonborn.