Ulrich I, Count of Celje

Little is known of Ulrich's early life. He was the firstborn son of Frederick, first Count of Celje, and his wife Diemut Wallsee. Frederick had inherited the Celje Castle and the surrounding estates through his mother Catherine, daughter of the last Carinthian Count of Heunburg (Vovbre, in Slovene) and Agnes of Baden, the unsuccessful claimant to the Babenberg inheritance.

The Counts of Celje owed their success to the allegiance to the Habsburgs. Like his father before him, Ulrich served as the Landeshauptmann (governor) of the Habsburg Duchy of Carniola from 1362.

Ulrich served as a condottiere, a military contractor lending his services to more powerful lords. He began his military career as a teenager when he joined the expedition of Hungarian king Louis the Great against the Venetians in Dalmatia in 1346, participating in the unsuccessful siege of Zadar.[5] In 1348, he fought in the service of Louis V, Duke of Bavaria in Tyrol and in Brandenburg.[6]

Despite beginning his career fighting against John Henry of Moravia in Tyrol, Ulrich eventually established strong ties with the Luxembourg rulers of Bohemia and Germany: in 1354, he took part in the expedition of the Holy Emperor Charles IV to Italy.[7] Likewise, he had strong ties to Louis the Great of Hungary, fightzing on his side against Venice in 1354–55, in the siege of Treviso.[8] Between 1359 and 1365, he took part of his expeditions to Serbia, Bulgaria and Southern Italy.[9][10] In 1362-63, he fought on the side of the Habsburg duke Rudolf IV in Friuli and in Tyrol; in reward for his service, he was pawned with Kamnik in Carniola, and Žalec and Vojnik in Styria: the latter two would remain in the possession of his descendendants until the House of Cilli would die out in 1456.[11]

The connection with the Hungarian and Polish king Louis proved fruitful. Ulrich's younger brother Hermann married Catherine of Bosnia, king Louis's sister in law, while Ulrich's son William married Anna of Poland, the daughter of Casimir the Great, the last Piast king of Poland. These marriages elevated the Counts of Celje into the circles of Central European royalty. At the same time, the settlement was convenient for Louis the Great who succeeded Casimir as King of Poland: Casimir's daughter, who might have otherwise claimed the throne for her children, was married off to Louis's loyal junior ally far away from Poland, thus neutralizing a potential challenge to his legitimacy in a problematic succession.[12]

Ulrich married Adelaide of Ortenburg, daughter of the powerful Carinthian count of Ortenburg. The marriage strengthened the alliance between the two houses. Only one son, William, survived into adulthood from this union. He married Anna of Poland, and had one daughter, Anna of Celje, who would become Polish queen consort by her marriage to Vladislav II.