The Kingdom of Skyy
Obscure legends abound with the origins of the Half-orc race. One story suggests that an ancient hobgoblin empire created half-orcs to lead orc tribes on the empire’s behalf. Yet another legend claims that a tribe of brutal human barbarians chose to breed with orcs to strengthen their bloodline. If you ask a half-orc about his origin, you might hear one of these stories. You might also just get a punch in the face for asking such a rude question.
Source: Player’s Handbook 2