He was half human/half demon. His demon side was strongest until he met and fell in love with Phoebe. As a demon, he could not help hurting the sisters. He asked Phoebe to strip (remove) his powers. After he helped vanquish the Source of All Evil, he became the new Source. In spite of Phoebe's love for Cole, she and her two sisters vanquish him, or so they thought. Cole came back and helped the sisters many times. Cole was eventually vanquished for good. Cole loved Phoebe very much. He would stop at nothing to win her back but he never succeeded.