Task: Question Answering
Input (English): Passage: At the end of the 15th century the Ottoman Empire advanced all over Southeastern Europe, eventually conquering the Byzantine Empire and extending control over the Balkan states. Hungary was the last bastion of the Latin Christian world in the East, and fought to keep its rule over a period of two centuries. After the tragic death of the young king Vladislaus I of Hungary during the Battle of Varna in 1444 against the Ottomans, the Kingdom was placed in the hands of count John Hunyadi, who became Hungary's regent-governor (1446–1453). Hunyadi was considered one of the most relevant military figures of the 15th century: Pope Pius II awarded him the title of Athleta Christi or Champion of Christ for being the only hope of resisting the Ottomans from advancing to Central and Western Europe. Question: Which Hungarian ruler was killed at the Battle of Varna?
Output (English): Vladislaus I