Final answer:
Heinrich Kramer developed the theory to include witchcraft in the purview of heresy inquisition.
Step-by-step explanation:
The correct answer is A) Heinrich Kramer. Heinrich Kramer was a German theologian and inquisitor who played a significant role in the witch-hunts of the 15th century. He co-authored the infamous book 'Malleus Maleficarum' ('Hammer of Witches') in 1486, which outlined the theory that witchcraft should be included within the purview of the inquisition for heresy.