Clark Ashton was the person who arranged the public display of the Necronomicon at the New York Public Library in 1984. Secretly, Ashton was the leader of the Cult of Cthulhu in New York, and had the book stolen so he could awaken his master. Although he was successful, the Ghostbusters were able to banish Cthulhu again, and Ashton was revealed and arrested.
Clark Ashton was named in homage of Clark Ashton Smith, a pulp author who was a friend of H.P. Lovecraft, as well as a Cthulhu Mythos author in his own right.