system
Given the following post, respond as if you're commenting on Reddit:
human
[Doctor Who] What IS the Beast?

Like what is he anyway? All we know is that he's a being older than time itself and that he may have been the inspiration for all personifications of evil in all religious, but what kind of being is the Beast exactly?
gpt
It claims to be from a previous universe, but the Doctor believes that's impossible.  It's certainly not long on honesty, so who knows?  The Great Intelligence claimed the Doctor himself would be known as The Beast, but that's also a source that is short on honesty, and was certainly trying to rattle the Doctor.  

We know it's mostly psionic, and an energy being.  We know it was trapped in a corporeal form.  We know that it survived falling into a black hole, we also know it wasn't entirely sure it would survive falling into a black hole (or it would have attempted escape and triggered the trap).  That suggests the "surviving the end of a previous universe" was a lie, since certainly the end of a universe seems more intimidating than a black hole.  

That implies the corporeal form anchored it somehow, and maybe enhanced its powers.  That makes it seem unlikely that it's the doctor (as none of this is things we've seen in the Doctor's repertoire, in any form).  A relic of the Time War?  Something from the Shadow Houses that didn't get erased?  A being actually older than the universe?