Who is Catalina, Later Known as Katherine, Queen of England from The Constant Princess and what is their importance?

Catalina is the daughter of Queen Isabella and King Ferdinand of Spain. She travels to England to marry Edward, her to the Tudor throne, who dies soon after their marriage and leaves her a widow. Catalina goes onto to marry King Henry VIII, give birth to a daughter, Mary (Bloody Mary), and later be divorced by her husband in favor of another woman.