You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Martin_Luther

Context:
In January 1519, at Altenburg in Saxony, the papal nuncio Karl von Miltitz adopted a more conciliatory approach. Luther made certain concessions to the Saxon, who was a relative of the Elector, and promised to remain silent if his opponents did. The theologian Johann Eck, however, was determined to expose Luther's doctrine in a public forum. In June and July 1519, he staged a disputation with Luther's colleague Andreas Karlstadt at Leipzig and invited Luther to speak. Luther's boldest assertion in the debate was that Matthew 16:18 does not confer on popes the exclusive right to interpret scripture, and that therefore neither popes nor church councils were infallible. For this, Eck branded Luther a new Jan Hus, referring to the Czech reformer and heretic burned at the stake in 1415. From that moment, he devoted himself to Luther's defeat.

Question:
Who was determined to expose Luther at this time?

Johann Eck