It was already a matter of record that they used Soul as a living, cybernetic computer that they ran data through...then I wondered if it might be connected with the Crossoverseers, the race that "Ringo", whom Lafferty met earlier, is the last competent survivor of.  (And of course, Ringo is playing a pivotal role in the CROSSOVERLORD.)

If there had been a member of that race protecting Lafferty's reality, once upon a time.  As all their race worked to keep realities separate, free to develop on their own.

I opted to go with a sort of crystalline being, mask-like in appearance like Ringo, yet different.  The Crossoverseers, the same race that Ringo belongs to, are extremely powerful---but their lifespans, though immense, is still liable to senility.  It sounds like this particular Crossoverseer had contacted the Zha'Tahn before, acting as mentor and guide.

In fact, one wonders if the Zha'Tahn's fiddling with humanity---turning some of them into superhuman weapons---may be because they fear that the rest of the Crossoverseer's race might come looking for vengeance.