Dirk IV was Count of Holland from 1039 to 1049. Dirk's date of birth is unknown but it was probably ca. 1030 or shortly before, he was described as "adolescent" at the time of his death. His base of operations was the stronghold his father built at Vlaardingen. Contemporary chroniclers referred to him as "Theodericus de Phlardirtinga" and as margrave thereof. The exact extent of his domain is not known, but at one time or another it stretched north to at least Rijnsburg and east to roughly Aalburg.
Dirk IV continued the policy of his father Dirk III to enlarge his possessions, developing and colonizing the low-lying peat areas of Holland and Utrecht. As a result, he came into conflict with the bishop of Utrecht, other bishops and monasteries in the surrounding area. Because of this, Emperor Henry III personally led an expedition against him in 1046, forcing Dirk to return some areas he had occupied. Shortly after the emperor had left however, Dirk started to plunder the territories of the bishops of Utrecht and Liège and made alliances with Godfrey III, Duke of Lower Lorraine and the counts of Hainaut and Flanders.