Johnny Depp is on board as a producer through his Infinitum Nihil production company. The comic book was created by Arvid Nelson and Eric Johnson, and centers on a world where the Protestant Reformation was defeated by the Catholic Church, and where magic is real. The story picks up in 1933 with a pathologist investigating the murder of a priest who took him in. This leads to a journey to find the Holy Grail.
Christi Dembrowski will also produce for Infinitum Nihil, along with Alan Riche, Peter Riche, and Mike Richardson. No production schedule was given for Rex Mundi.