Justiciar is the English form of the medieval Latin term justiciarius or justitiarius (meaning "judge" or "justice").[1][2] The Chief Justiciar was the king's chief minister, roughly equivalent to a modern Prime Minister of the United Kingdom.[3]
The Justiciar of Ireland was an office established during the Anglo-Norman invasion of Ireland and was a key tool in its colonisation. Following the conquest of the Principality of Wales in the 13th century, the areas that became personal fiefs of the English monarchs were placed under the control of the Justiciar of North Wales and the Justiciar of South Wales.
A similar office was formed in Scotland, although there were usually two or three – the Justiciar of Scotia, the Justiciar of Lothian and, in the 13th century, the Justiciar of Galloway. These offices later evolved into a national one called Lord Justice-General. The modern title is Lord President of the Court of Session.
Similar positions existed in continental Europe, particularly in Norman Italy and in Sweden.