My theories are as follows
1. The Qunari Sarabaas woke him when he activated his mask in the Redemption Web Series (very very similar to the orb btw and easy to activate so not sure why Solas couldn't do it himself if that was the way he intended it activated. The mask needed elvhen blood though while the orb seemed to do ok with human blood). Then he went about trying to find a way to activate his orb. Fen'Harel probably had a plan to get rid of Corypheus once he had him in the fade that went up in smoke when you took the key. He took the name Solas because he was proud enough to think he could trick the magister and ended up killing a ton of people instead.
2. After fighting Hawke Corypheus went looking for ways back to the black city. I assume the magisters had compiled a list of ways into the fade and the orb was one of them. I would also assume Fen'harel was asleep before the first blight. If this is true then Corypheous woke him up and demanded the orb which Fen'Harel gave him because he was too weak to do anything else. then he followed Coypheus looking for a way to get it back.
Also not sure "the people" are the elves he spends a lot of time talking smack about the elves with Lavellan.