Final answer:
Henry VIII was given the ironic nickname 'The Great Schismatic' by the Roman Catholic Church.
Step-by-step explanation:
Henry VIII's ironic nickname given by the Roman Catholic Church was The Great Schismatic. Initially, Henry was granted the title 'Defender of the Faith' by Pope Leo X for his opposition to the Reformation. However, when the Pope refused to annul Henry's marriage to Catherine of Aragon, Henry created the Church of England and broke away from the Roman Catholic Church, earning him the nickname 'The Great Schismatic'.