I've already read about Rasputin in the other post, but one solid fact that I'm sure of is that, in the past Rasputin sensed the darkness outside our Solar System, and as you mentioned there were 8 Warminds, that's one for every planet it would make sense for Pluto to be the farthest, but I don't know whether the Golden Age colonized it or Mercury. Either way for Rasputin to know the Darkness was coming and survive, not to mention it assumed control "like Harbinger" and fought the Darkness however possible and survived. Now present day with our Guardians,we awaken the old Warmind, crippled like the Traveler, but still capable and without any explanation because all Rasputin does is play music, he starts to regain control/build his sphere of influence pre-Collapse, on Venus he takes control, and on Mars, he takes control. Rasputin is trying to assess the damage the Darkness did by rebuilding himself or atleast by retaking the Solar system, and uncovering old systems locked away,without the help of the City or Guardians he won't make it very far. Sadly though I just remembered Rasputin is riding his quest solo, probably because it's the only thing around that actually knows what it's doing.