His early years were passed amid the anarchy which prevailed everywhere in the country, after several struggles, in which he took part, he was recognized as ruler of Bohemia by the emperor Henry VI in 1192. He was, however, soon overthrown for joining a conspiracy of German princes to bring down the Hohenstaufen monarchy. In 1197 Otakar forced his brother, duke Vladislav Jindřich, to abandon Bohemia to him and to content himself with Moravia. Taking advantage of the German civil war between the Hohenstaufen claimant Philip of Swabia and the Welf candidate Otto IV, Ottokar declared himself King of Bohemia. This title was supported by Philip of Swabia who needed Czech military support against Otto (1198).
In 1200 - with Otto IV in the ascendancy, Otakar abandoned his pact with Philip and declared for the Welf faction. Both Otto and Pope Innocent III subsequently accepted Otakar as hereditary King of Bohemia.
Philip's consequent invasion of Bohemia was successful. Otakar, having been compelled to pay a fine, again ranged himself among Philip's partisans and still later was among the supporters of the young king, Frederick II. In 1212 Frederick granted the Golden Bull of Sicily to Bohemia. This document recognised Otakar and his heirs as Kings of Bohemia. The King was no longer subject to appointment by the Emperor, and was only required to attend Diets close to the Bohemian border. Although a subject of the Holy Roman Empire, the Bohemian King was to be the leading electoral prince of the empire and to furnish all subsequent Emperors with a bodyguard of 300 knights when they went to Rome for their coronation.
Otakar's reign was also notable for the start of German immigration into Bohemia and the growth of towns in what had until that point been forest lands. In 1226 Otakar went to war against Frederick II of Austria after the latter wrecked a deal which would have seen Otakar's daughter (Saint Agnes of Bohemia) married to Emperor Frederick II's son, Henry II of Sicily. Otakar then planned for the same daughter to marry Henry III of England, but this was vetoed by the Emperor who knew Henry to be an opponent of the Hohenstaufen dynasty. Then widowed Emperor himself wanted to marry Agnes, but by then she didn't want to play a role in an arranged marriage anymore. With the help of the pope, Agnes entered the convent.
