If a work has both an author and an illustrator, the order of elements in your citation will depend on which of those persons you emphasize in your paper.
Author first: Complete works cited entry
Gaiman, Neil. The Sandman: Overture. Illustrated by J. H. William III, DC Comics, 2015.
Illustrator first: Complete works cited entry
Kerascoët, illustrator. Beautiful Darkness. By Fabien Vehlmann, Drawn and Quarterly, 2014.
Author and illustrator the same: Complete works cited entry
Ulinich, Anya. Lena Finkle’s Magic Barrel: A Graphic Novel. Penguin Books, 2014.
General guidelines for the MLA works cited list
Directory to MLA works cited models
How to answer the basic question “Who is the author?”