In Medieval England and Scotland the Chief Justiciar (later known simply as the Justiciar) was roughly equivalent to a modern Prime Minister as the monarch's chief minister. Similar positions existed Continental Europe, particularly in Norman Italy and in the Carolingian empire. The term is the English form of the medieval Latin justiciarius or justitiarius ("man of justice", i.e. judge).
A similar office was formed in Scotland, though 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 Justiciar of Ireland was an office established during English rule. (See Lord Chief Justice of Ireland).
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.
In the Kingdom of England the term justiciar originally referred to any officer of the King's Court (Curia Regis), or, indeed, anyone who possessed a law court of his own or was qualified to act as a judge in the shire-courts. In each English shire, the sheriff was the king's representative in all matters. The only appeal against decisions of the sheriff or his courts was to the king. During the reign of William Rufus many sheriffs were severely overworked; Rufus eased the burden by appointing local justiciars in some shires.