The Bugbear is an existing mythological beast! I adore DnD thanks to its unifying multiple monsters using stats. In this case, the Bugbear is a bogeyman of Medieval England. They took the shape of bears, aiming to frighten and eat children lingering in the forests at night. Like most bogeymen, they were invented to keep children from misbehaving and winding up bear food. A bear, for some reason, wasn't intimidating enough.