The first four titles in my series have done just that. Calvin, Augustine, John Owen, and Athanasius have all been instrumental in the understanding and development of very important tenets of the Christian faith.
It is, however, time to include a woman, and it's hard to keep the same criteria in my choice. Women were esteemed in the early church. My favorite is Marcella of Rome, a rich and very educated woman who was eager to learn all she could about Christian doctrine and became a great influence on Jerome and on Roman women of her time. Still, we can't say she impacted the church and its doctrines.
I don't remember how the choice fell on Lady Jane. I had her in my list of prospective titles, and the publisher thought she was a good idea. I couldn't say she had a monumental impact on the church either. Still, telling her life will give me the opportunity to show how God preserved His people and doctrine in England during the difficult transition from a Roman Catholic to a Protestant church.
I foresee some difficulties. There is much myth and hagiography around the figure of Lady Jane, but I am confident that the Lord will help me as He has done until now.