From Classic Encyclopedia 1911
JUSTICIAR (med. Lat. justiciarius or justitiarius, a judge), in English history, the title of the chief minister of the Norman and earlier Angevin kings. The history of the title in this connotation is somewhat obscure. Justiciarius meant simply "judge," and was originally applied, as Stubbs points out (Const. Hist. i. 389, note), to any officer of the king's court, to the chief justice, or in a very general way to all and sundry who possessed courts of their own or were qualified to act as judices in the shire-courts, even the style capitalis justiciarius being used of judges of the royal court other than the chief. It was not till the reign of Henry II. that the title summus or capitalis justiciarius, or justiciarius totius Angliae was exclusively applied to the king's chief minister. The office, however, existed before the style of its holder was fixed; and, whatever their contemporary title (e.g. Custos Angliae), later writers refer to them as justiciarii, with or without the prefix summus or capitalis (ibid. p. 346). Thus Ranulf Flambard, the minister of William II., who was probably the first to exercise the powers of a justiciar, is called justiciarius by Ordericus Vitalis.
The origin of the justiciarship is thus given by Stubbs (ibid.
p. 276). The sheriff "was the king's representative in all matters judicial, military and financial in the shire. From him, or from the courts of which he was the presiding officer, appeal lay to the king alone; but the king was often absent from England and did not understand the language of his subjects. In his absence the administration was entrusted to a justiciar, a regent or lieutenant of the kingdom; and the convenience being once ascertained of having a minister who could in the whole kingdom represent the king, as the sheriff did in the shire, the justiciar became a permanent functionary." The fact that the kings were often absent from England, and that the justiciarship was held by great nobles or churchmen, made this office of an importance which at times threatened to overshadow that of the Crown. It was this latter circumstance which ultimately led to its abolition. Hubert de Burgh was the last of the great justiciars; after his fall (1231) the justiciarship was not again committed to a great baron, and the chancellor soon took the position formerly occupied by the justiciar as second to the king in dignity, as well as in power and influence. Finally, under Edward I. and his successor, in place of the justiciar - who had presided over all causes vice regis- separate heads were established in the three branches into which the curia regis as a judicial body had been divided: justices of common pleas, justices of the king's bench and barons of the exchequer.
Outside England the title justiciar was given under Henry II. to the seneschal of Normandy. In Scotland the title of justiciar was borne, under the earlier kings, by two high officials, one having his jurisdiction to the north, the other to the south of the Forth. They were the king's lieutenants for judicial and administrative purposes and were established in the 12th century, either by Alexander I. or by his successor David I. In the r 2th century a magister justitiarius also appears in the Norman kingdom of Sicily, title and office being probably borrowed from England; he presided over the royal court (Magna curia) and was, with his assistants, empowered to decide, inter alia, all cases reserved to the Crown (see Du Cange, s.v. Magister Justitiarius). See W. Stubbs, Const. Hist. of England; Du Cange, Glossarium (Niort, 1885) s.v. " Justitiarius."