Final answer:
Thomas Cranmer was the Archbishop of Canterbury who supported Henry VIII's break from the Catholic Church and introduced Protestant reforms in the Church of England.
Step-by-step explanation:
The Archbishop of Canterbury who helped build Henry VIII's case for breaking from the Catholic Church and annulling his marriage to Catherine of Aragon was Thomas Cranmer. During the reign of Edward VI, Cranmer introduced major Protestant reforms within the Church of England and wrote the Book of Common Prayer. Unfortunately, he was later executed during the reign of Mary I.