The Leonine Misbegotten is the boss of Castle Morne, down at the extreme southern end of the Weeping Peninsula. It is the legacy dungeon of the area.
This is likely the easiest legacy dungeon in the game, being full of demihumans, and the Leonine Misbegotten, while relatively fast and agile, is not a very difficult boss; beyond sheer aggression, he doesn't have a lot of tricks, and he can be overwhelmed with nothing more than basic demi-human ashes and a +2 weapon.
The sword he drops has a strength requirement of 40 and has rather slow swings, though its hits are quite meaty.