Facts and Events
He succeeded his father in 1105. In 1121 he married Judith of Bavaria, a member of the powerful House of Guelph. On the death of Emperor Henry V, his uncle, Frederick stood for election as King of the Romans with the support of his younger brother Conrad, duke of Franconia and several houses. However, he lost this election of 1125 to Lothar III, crowned Emperor later in 1133.
A conflict erupted between Frederick and his supporters, and Lothar. Encouraged by Adalbert of Mainz, who loathed the supporters of the late Emperor Henry V, Lothar besieged Nuremberg in 1127. Frederick relieved the siege of Nuremberg in 1127 and occupied Speyer in 1128. The attempt of Henry the Proud, duke of Bavaria, to capture Frederick during negotiations failed (1129). However, afterwards supporters of Lothar won a number of victories both in Germany and in Italy. Speyer (1129), Nuremberg (1130) and Ulm (1134) were captured and in October 1134 Frederick submitted to the emperor. In 1135 both Frederick and Conrad were finally reconciled with Lothar. After Lothar's death (1137) and election of Conrad as King of the Romans (1138) Frederick supported his brother in the struggle with Guelphs. According to Otto of Freising, Frederick was "so faithful a knight to his sovereign and so helpful a friend to his uncle that by valor he supported the tottering honor of the realm, fighting manfully against its foes..."
Frederick's second wife, Agnes, was the niece of his old enemy Albert of Mainz.