The Enemy

The Enemy were the Time Lords' largely unseen opponents in the War. Little was known about them. It could not even be said, for instance, whether the term described a species or merely a group of individuals.

Greyjan the Sane claimed that they were ancestor cells which had been irradiated by temporal interference and then energised by a leaking bottle universe. The Eighth Doctor offered the more entertaining possibility that they were likely to be eventually revealed as "Yartek, leader of the alien Voord, carrying a big stick." (PROSE: The Ancestor Cell)

They were known to be neither the Daleks nor the Krotons. (PROSE: Alien Bodies)

The Enemy's agents were referred to as "reps", but there was no indication what, if any, significance the term had. (PROSE: The Taking of Planet 5)

Behind the scenes

 * Despite reports to the contrary, the Enemy were never originally planned to be the Daleks. Other books in the Eighth Doctor Adventures series make it clear that the Enemy cannot be the Daleks. The confusion arose in relation to a later BBC Books arc, culminating in Sometime Never..., which had been intended to feature the Daleks until legal issues prevented it.
 * Lawrence Miles intended to reveal who the Enemy were in the next novel he wrote, but editor of the range at the time Stephen Cole prevented him from doing so.