Frederick I (1145–1167) was duke of Swabia, succeeding his cousin Frederick Barbarossa in 1152.
He was the son of King Conrad III of Germany and his second wife Gertrude von Sulzbach and thus the direct heir of the crown, had there been true heredity. However, on his death bed, Conrad III allegedly advised the only two persons present, his nephew Frederick Barbarossa and the bishop of Bamberg, to nominate Frederick Barbarossa; and handed the Imperial insignia to him.
Conrad III (German: Konrad; Italian: Corrado; 1093 or 1094 – 15 February 1152) of the Hohenstaufen dynasty was from 1116 to 1120 Duke of Franconia, from 1127 to 1135 anti-king of his predecessor Lothair III, and from 1138 until his death in 1152 King of the Romans in the Holy Roman Empire. He was the son of Duke Frederick I of Swabia and Agnes, a daughter of Emperor Henry IV.
His reign saw the start of the conflicts between the Guelphs and Ghibellines. He was involved in the failed Second Crusade with Louis VII, where he would fight and lose at Doryleum and would later fall ill and return to Constantinople. After recuperating, he went to Jerusalem but would experience a string of failed sieges. Later returning from the Crusade, he was entangled in some conflicts with Welf VI's claim to the Duchy of Bavaria. On his deathbed, he designated his nephew Frederick Barbarossa as his successor instead of his son, Frederick IV, Duke of Swabia.
Frederick Barbarossa was elected King of Germany on 4 March 1152 in Frankfurt am Main. Frederick's uncle, Otto of Freising, was an eyewitness and is the most important source for the 1152 election. According to him, "the entire company of the princes ... from the immense extent of the transalpine realm (as well as certain barons from Italy)" met in Frankfurt by early March to elect a successor to King Conrad III, who had died barely two weeks earlier at Bamberg on 15 February 1152. Only five days after his election, on 9 March, Frederick was crowned in the Aachen Chapel.
The apparent quickness of the election of 1152 contrasts with those of 1125 and 1138. In his own letter to Otto of Freising listing the accomplishments of his first five years on the throne, Frederick does not mention his election, but says only that "we were anointed at Aachen and received the crown of the German realm." According to Otto, Conrad had on his deathbed designated Frederick as his choice of successor, because he knew that the princes would not elect his young son, Frederick. He then entrusted his son and the royal insignia to Frederick.