The Nemesis is the adversary of the Eternal Entity. Roger Wilco discusses the Nemesis not long after traveling to the future as a possible explanation for strange writing in the horizon which explained the era he had travelled to. If it was not from the Eternal Entity it might have been put there by the Nemesis instead. If that was true Roger believed that they both had the same adversary, and that the Nemesis true name could only be Sludge Vohaul (or possibly in cahoots). However, Roger was not completely sure, and couldn't rule out the possibility that the writing could just be a side affect of time travel.