What kind of people wore African masks?

For instance kings, leaders, etc.What kind of people wore African masks?
The British Museum in London has a collection of them - have a look at the website and see if there are detailed descriptions. I think they would be mainly used in rituals by priests, but of course Africa is a whole large continent and there may be great differences. I found several interesting sites when I googled, including one called Masks of Africa, which may be quicker than going through the British Museum's collection.