Who is Thomas Seymour from The Six Wives of Henry VIII and what is their importance?

Thomas Seymour was the brother of Henry's third wife, Jane Seymour. He was ambitious, manipulative, and not above encouraging his sister to engage the King, even though he was married. After Jane's death, Thomas continued to be a presence in the court, as well as a constant in the life of the Prince of Wales..... his nephew.