Basically Rasputin helps you take down some frozen hive with an energy lance and then reactivates the solar systems WARSAT system. He declares he will defend humanity on his own terms and has no equal.
Yeah pretty much what hes been doing all along, nothing was explained or revealed about his history. What a waste. I'm done with bungie. The campaign was 3 missions no more than 30 min long worth of content. It was shorter than CoO. The Queen and Rasputin were the two most interesting aspects of the destiny world and both got less than stellar expansions across 2 games. Instead we got more hive shit. The only interesting thing in this expac is SUROS Regime is back.