Not the darkness because it is in the "allies" section of the grimoire and we are not allied with the darkness. Don't think it's the traveler because I don't. What we know about Rasputin: last of the warminds, incredibly intelligent, survived the collapse, was made to fight enemies of the light. Pretty much fits everything in the grimoire. Plus you can look up the titanomachy (basically battle of gods). Sounds more like the traveler and the darkness while the narrator is a third party who witnessed it.