The suffix "hus" (meaning house) was commonly used for castles in medieval Denmark (Koldinghus, Tønderhus, Ålborghus, Riberhus etc.).
The castle was the home of the governor of the borough (and later the county), who took care of the king's (or in Southern Jutland, the duke's) possessions, in and around the city.
When Hans the Elder was proclaimed Duke of Slesvig and Holstein (today Southern Jutland and Northern Germany), he took up residence in Haderslevhus, which now, in 1544, was an old and worn-out building.
In the 1570s, Duke Hans the Elder proceeded to build the eastern and northern wings of Hansborg, but he died in 1580, and therefore did not see the completed castle.
After the Duke died, King Frederick II of Denmark acquired parts of his lands, including Haderslev, and in 1580-1585, he finished the construction of the last two wings.