Gen13/Monkeyman and O'Brien is a two-issue comic book miniseries published by Image Comics in 1998. It serves as a crossover between Art Adams's creator-owned Monkeyman and O'Brien and WildStorm's Gen13.
The story is an homage to the Star Trek episode "Mirror, Mirror", with a transporter incident swapping many of the titular cast members with their evil counterparts from an alternate universe.
References Gen13/Monkeyman and O'Brien @ comicbookdb Gen 13/Monkeyman & O'Brien at the DC Database