An adherant of the Church of the Brethren, a Christian pietist group founded by Alexander Mack in Germany in the early 1700s in protest of the religous excesses he saw at the time. The term is from the German "Tunker," and refers to the trine baptism whereby converts were "dunked" or baptized three times, once each for the Father, the Son, and the Holy Ghost. Also called Dunkards.

Many members of the Church of the Brethren migrated to the U.S. in the 1700s to avoid religious persecution and settled among similar-minded Quakers and Mennonites in Pennsylvania and western Maryland and Virginia. The term Pennsylvania Dutch rightly applies to many Dunkers, but Dunkers also won English-speaking adherants among their neighbors. Many Dunkers joined the migrations to newly-opened western lands in the early 1800s and later.

The Dunker Church at Antietam, Maryland, was a focal point of the Civil War battle fought there in 1862, in the middle of a pacifist community. It has been rebuilt and is now under administration of the National Park Service.

The Church of the Brethren survives today in the U.S. and elsewhere. A good modern web reference is the unofficial Church of the Brethren Network or COBnet at http://www.cob-net.org/.