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:
Mary_(mother_of_Jesus)

Context:
Roman Catholics believe in the Immaculate Conception of Mary, as proclaimed Ex Cathedra by Pope Pius IX in 1854, namely that she was filled with grace from the very moment of her conception in her mother's womb and preserved from the stain of original sin. The Latin Rite of the Roman Catholic Church has a liturgical feast by that name, kept on December 8. Orthodox Christians reject the Immaculate Conception dogma principally because their understanding of ancestral sin (the Greek term corresponding to the Latin "original sin") differs from the Augustinian interpretation and that of the Roman Catholic Church.

Question:
Which pope proclaimed the Immaculate Conception of Mary?

Pope Pius IX