The graphic novel has become one of the most popular forms of print books, generating more than a billion dollars in sales.

And the medium features a broad base of characters and topics — from superheroes like Batman to real-life heroes like civil-rights leader John Lewis, who was featured in a recent series.

Award-winning author and illustrator Mark Siegel, founder of First Second Books, is in the Valley to lecture on "The Great American Graphic Novel" and to lead a workshop for ASU’s Center for Science and the Imagination.

We spoke with Siegel about the impact of graphic novels.