What is an egwugwu?

In the story, Things Fall Apart, by Chinua Achebe, egwugwu are the spirits of the ancestors of Nigerian tribes. Great men of these tribes wear masks that can have a rather terrifying look about them, which is exactly how it is supposed to make you feel.

The most disgraceful things you can do to an egwugwu would be to unmask it in public, which kills the spirit. When an egwugwu dies, the mother spirit cries a dreadful cry for the death of her son for a week.

The egwugwu were also summoned whenever the villagers needed to settle disputes in a court. The spirits of the ancestors were said to be the highest judges in the land.