Ulrich II, or Ulrich of Celje, was the last Princely Count of Celje. At the time of his death, he was captain general and de facto regent of Hungary, ban (governor) of Slavonia, Croatia and Dalmatia and feudal lord of vast areas in present-day Slovenia, Croatia, Bosnia, Austria, and Slovakia. He was also a claimant to the Bosnian throne. He was killed by agents of the Hunyadi clan under unknown circumstances, which plunged Hungary into civil unrest that was resolved a year later by the sudden death of king Ladislas the Posthumous and the election of Matthias Corvinus, the son of John Hunyadi and Ulrich's son-in-law, as king. Ulrich's possessions in the Holy Roman Empire were inherited by Emperor Frederick III, while his possessions in Hungary were reverted to the crown.

The Counts of Celje or the Counts of Cilli were the most influential late medieval noble dynasty on the territory of present-day Slovenia. Risen as vassals of the Habsburg dukes of Styria in the early 14th century, they ruled the County of Cilli as immediate counts (Reichsgrafen) from 1341. They soon acquired a large number of feudal possessions also in today's Croatia and Bosnia. They rose to Princes of the Holy Roman Empire in 1436. The dynasty reached its peak with Ulrich II of Cilli, but with his death in 1456 they also died out, and after a war of succession, the Habsburgs inherited their domains.