We still haven't figured out who Star Trek: Discovery's Red Angel is, but we have an interesting theory about the malevolent race behind the total annihilation of the Federation: the Kelpiens. If we take their subplot from several weeks ago as foreshadowing, it's easy to see how they clearly evolve to become the galaxy's worst villains in just a few short centuries.
Before the Kelpien rule of Kaminar fell to the Ba'ul, they were, by all accounts, ruthless predators. By instituting forced executions a.k.a. "The Great Balance" among the Kelpiens, the Ba'ul ensured the race never grew out of their docile states into the fierce conquerors they once were. But when Saru escaped the planet and was allowed to age beyond his Vahar'ai, he realized the truth of what the Ba'ul had instituted and returned to Kaminar to liberate his people with the help of Discovery. Pike protested that Starfleet interference would constitute a violation of the Prime Directive and could potentially cause the extinction of the Ba'ul down the line, should the Kelpiens resort to their former ways. Burnham was successful in convincing him that it would take generations for the Kelpiens to develop the technology that would enable them to threaten the Ba'ul, and Saru assured Pike that the Kelpiens would use that time to show the Ba'ul the Kelpiens intended to share Kaminar peacefully.
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But what if that's not what happened? Given that the Kelpiens would be in possession of literal centuries of collective unconscious rage, and no one stuck around to monitor the progress on the planet, what was there to stop the Kelpiens from evolving into their former aggressive state, and then taking that aggression off-world?
While it might seem silly to think of the erstwhile meek and benign race as the devious minds behind the large scale destruction the probe aliens are set to dole out, it's certainly within the realm of possibility that the Kelpiens turn into that kind of species. Ideally, they would've learned from their past mistakes as a civilization, but centuries of forced execution and manipulation at the hands of another race would ensure at least a few Kelpiens would not only desire vengeance, but feel entitled to it as well. And evolution is typically not a process of societies learning from their past mistakes and never repeating them - quite the opposite, in fact.
If we treat the Kelpien storyline as foreshadowing instead of subplot, Burnham's insistence that it would take Saru's race "generations" to catch up to Ba'ul technology all of a sudden becomes disturbingly prophetic. What if that's exactly what happens? What if the Kelpiens gradually retain dominance of Kaminar and ultimately decide they don't want to stop there? Also, it feels highly unlikely that either the Red Angel or the probe aliens will turn out to be a person or race we've yet to encounter. The mystery surrounding the identity of both entities has been too far built-up for its solution to be a random, malevolent race we've never encountered before. It also seems unlikely - at least in the case of the aliens - that the solution will be a race like the Borg or the Sphere Builders from another series.
Only a race we've seen on Discovery will feel as resonant as it needs to be to make for a satisfying conclusion to this arc. To be fair, that's far from a confirmation that the Kelpiens evolve into genocidal maniacs, but it's interesting to note that they're certainly capable of that.