Henry IV (II) the Faithful (Polish: Henryk IV (II) Wierny) (c. 1292 – 22 January 1342) was a Duke of Żagań and parts of Greater Poland from 1309 until 1317 (with his brothers in all the lands except Głogów in different divisions among them), Duke of Głogów from 1318 until 1321 (with his brother as co-ruler) and sole ruler over Żagań from 1321 until his death.

Although he was seventeen years old, an age considered enough to rule alone according to the Piast dynasty customs, for unknown reasons, he remained, with his immediate younger brother Konrad, under the regency of their mother until 1312.

In 1312 Henry IV made the first division of the duchy: the eastern part, consisting of the towns of Oleśnica, Kluczbork, Kalisz and Gniezno was given to his younger brothers Konrad and Bolesław.

Henry IV and his youngest brothers Jan and Przemko II retained Ścinawa, Żagań and Greater Poland.

The situation of the dukes of Głogów was difficult from the beginning of their rule, mostly because of the revived pretensions of Władysław I the Elbow-high over all Greater Poland and the inheritance of Henry IV Probus.

In the marriage contract the towns of Krosno Odrzańskie and Żagań were also pledged to the Margraviate, remaining in the hands of Brandenburg until 1319, when they came back to Henry III's sons.

Thanks to this alliance with the House of Ascania Henry IV, along with younger brothers Konrad and Bolesław renounced in Berlin on 3 March 1310 their claims over Gdańsk Pomerania to the Margraves Waldemar of Brandenburg-Stendal and John V of Brandenburg-Salzwedel, who soon sold them for a large sum of money to the Teutonic knights.

The situation worsened two years later, when the dukes of Głogów were excommunicated by the Archbishop of Gniezno, Jakub Świnka and the Bishop of Poznań, Andrzej Zaremba.

The war of 1312–1317 was finally ended with the settlement of 8 January 1317, by which the dukes of Głogów were forced to cede the territory between the Oder River and Wołów, with Uraz and Lubiąż.

On 29 July 1326 Henry IV concluded a treaty with his brothers Jan of Ścinawa and Przemko II of Głogów, according to which if one of them died without male issue, the other two inherited his land.