Quakers were some of the very first and most vocal critics of slavery.

the definition of a a Quaker is:

"a member of the Religious Society of Friends, a Christian movement founded by George Fox c. 1650 and devoted to peaceful principles. Central to the Quakers' belief is the doctrine of the "Inner Light," or sense of Christ's direct working in the soul. This has led them to reject both formal ministry and all set forms of worship."

Some information could be:

Quakers, also called Friends, are a historically Christian group whose formal name is the Religious Society of Friends. Members of the various Quaker movements are all generally united in a belief in the ability of each human being to experimentally access the light within, or "that of God in every one".

Associations: Britain Yearly Meeting, Friends

Origin: Mid-17th century; England

Separated from: Church of England