Prinz Eisenherz
The subject matter of Toonopedia overlaps with the books Markstein wrote, edited and compiled. "A Prince Valiant Companion" (Manuscript Press, 1992), by Todd Goldberg and Carl J. Horak, was edited by Markstein and Rick Norwood. It includes plot summaries of the "Prince Valiant" comic strip from its beginning in 1937 to the 1980 retirement of the strip's creator, Hal Foster, along with additional material on the series and Foster's other work.