A bishop is an ordained member in a religious institution, who is entrusted with a position of authority and oversight. In traditional Christianity, i.e., existing denominations that predate the Protestant Reformation, bishops claim apostolic succession, a direct historical lineage dating back to the original Twelve Apostles. The bishops are by doctrine understood as those who possess the full priesthood given by Jesus Christ, and therefore may ordain other clergy, including other bishops. A person ordained as a deacon, priest, and then bishop is understood to hold the fullness of the (ministerial) priesthood, given responsibility by Christ to govern, teach, and sanctify the Body of Christ. Priests, deacons and lay ministers co-operate and assist their bishops in pastoral ministry.