Mother Malkin is the primary antagonist in the book series The Wardstone Chronicles and in its 2015 film adaptation Seventh Son.
In the movie, Malkin is a very dangerous creature. Many years ago, she was captured by John Gregory, but was freed. She regrouped with her sister, Lizzie, and her followers, including Radu, and aimed to take over the world. She was ultimately killed by Tom Ward.
In the books
In the book series, she is also the primary antagonist and was also captured by the Spook (like in the movie).