His father Gebhard of Supplinburg joined the Saxon rebellion against the ruling Salian dynasty and died on 9 June 1075 in the Battle of Langensalza, fighting troops loyal to emperor Henry IV.

[8][9] Lothair's land purchases, inheritance and marriage alliances among the Saxon nobles, resulted in the acquisition of the domains of the House of Billung and the Counts of Northeim.

For his loyalty Lothair was rewarded with the fief of title and estate of the Duchy of Saxony upon the death of duke Magnus of Billung, who had died without an heir in 1106.

[10] Emboldened by the promotion and incensed over the king's increasingly autocratic rule, such as the wanton imposition of a new tax on ducal lords, Duke Lothair joined the growing opposition party to Henry.

He was soon reinstated when count Otto fell into disgrace and he tactically submitted himself to Henry V. In 1115 however, he took command of the rebellious Saxon forces and defeated the emperor in the Battle of Welfesholz.

On August 24 the electors declined the candidacy of the primary contender Duke Frederick of Hohenstaufen, who destroyed his chances due to his appalling overconfidence (ambicone cecatus) and his refusal to accept free princely elections (libera electio).

[14] His election was notable in that it marked a departure from the concept of hereditary succession as the electors preferred a sovereign with moderate powers after the Salian era of oppressio.

[15] Somewhat naive concerning the complex power struggle between the papacy and the empire, Lothair also consented to several symbolic acts that were subsequently interpreted by the Roman Curia as signaling acceptance of papal confirmation of his position.

The succession was disputed among his surviving brother Soběslav I and his Moravian cousin Otto the Black, who was supported by Vladislaus' widow Richeza of Berg.

[17] A military campaign against Soběslav was launched and in February 1126 Lothair's force entered Bohemian territory and was promptly defeated at the Battle of Chlumec.

Peace was restored, prisoners set free and although the winner of the battle had submitted himself to the losing side, he secured full legitimacy and lasting prestige.

Lothair, with the approval obtained at a meeting of the princes in Regensburg, attempted to seize the crown lands, which provoked a Staufer reaction.

Conrad, on the other hand failed to acquire the desired assistance in Italy, and having made no political progress, returned in 1130, which assured at least a partial victory for Lothair.

[20][21] Lastly Lothair, in order to prevent the loss of Burgundy to a power hostile to the empire, appointed his loyal ally Conrad I, Duke of Zähringen as Rector of the Principatus Burgundiaey.

He already pursued active territorial policies before his royal tenure as early as 1111, when he installed count Adolf of Schauenburg in Holstein and Stormarn.

Subsequently the Franks desired to rule the acquisition, which proved to be only partly successful, as a long process of depopulation and recurring population replacement by Franconians, Bavarians and Christianized Slavs followed.

Lothair's diplomatic missions to the warring parties of Poland and Bohemia/Hungary were successful and resulted in overdue tribute payment by the Polish Duke Bolesław III Wrymouth for the 1121 established Duchy of Pomerania, which in addition to the island of Rügen was eventually secured as a fief of the Empire.

[27] In March 1131 these three met in Liège, where Lothair performed the ceremonial strator service (stirrup holder) for the pope and promised help in the conflict against Anacletus and Roger II of Sicily.

He ignored Innocent's bull, in which he advocated imperial authority derived from him and Lothair recognized papal claims to the vast Matildine estates in Northern Italy (formerly owned by Margravine Matilda of Tuscany), although he was able to secure the territorial fiefs.

Anti-king Conrad renounced his royal title,[32] The Staufers promised to take part in the Emperor's second Italian campaign, before a ten-year constitutio pacis was declared.

His body was boiled to prevent putrefaction,[37] and his bones were transferred to the Collegiate Church of Saints Peter and Paul at Königslutter, which he had chosen as his burial site and for which he had laid the cornerstone in 1135.