Otto IV. was the son of Henry the Lion and was crowned, as the only Guelph ever, Emperor of the Holy Roman Empire on the 4th of October 1209. He came from one of the most influential and powerful families of his time. He found his final resting place in the collegiate church of his father which is today St. Blasii Cathedral. His parents and his first wife, Beatrix, are also buried there.

The history of Braunschweig is closely linked with the story of this Guelph emperor. The time of his reign was a decisive period for Braunschweig and the region. Henry the Lion and his son laid down the foundations for the town's development at the turn of the 12^th to the 13^th century. Otto IV. certainly left his mark and some of those traces can still be found today. For example, he finished the construction of St. Blasii Cathedral, extended the city wall and built12 city gates.