The last Catholic of the Welf princes, he was known for the large number of wars in which he was involved and for the long-standing affair with his mistress Eva von Trott.

When in 1542 Elector John Frederick I of Saxony and Landgrave Philip I of Hesse as members of the Protestant Schmalkaldic League came to the help of Goslar, they managed to occupy the complete Principality of Wolfenbüttel.

But in October he was captured by Hessian troops and kept prisoner,[1] until the Emperor finally defeated the Schmalkaldic League at the Battle of Mühlberg, freed Henry and reinstated him in 1547.

[2] Henry's affair with his mistress Eva von Trott (1506–1567), a lady-in-waiting to his consort Maria of Württemberg, produced ten children [1522-1558].

When rumours about his amour spread, he pretended she had died and arranged for a feigned funeral at Gandersheim Abbey, while she hid in Liebenburg Castle.