[3] In 1088[4] or 1089,[5] when Welf was still a teenager, he married Matilda of Tuscany,[3] who was more than twenty years older than him, in order to strengthen the relation between his family and the pope during the Investiture Controversy between king and pope.

It is not clear whether Welf left Matilda, or vice versa.

[7] It is possible that Welf left Matilda after he found out that she had willed her lands to the papacy and he could not expect to inherit them.

[9] After his father's death in 1101, Welf inherited the office of duke of Bavaria.

He was succeeded as duke of Bavaria by his younger brother, Henry IX.