Michael took possession of Deans Body, in order to kill Lucifer. According to Dean it was a 'one time deal'. But Michael betrayed him, he took possession of him and escaped after killing Lucifer.

He was building his own army of monsters, doped with his archangel grace.

After Michael mysteriously left Deans Body, the boys - including you - thought it‘s over. But Michael made a comeback, he took advantage of Deans body and then he broke the only weapon that can kill him.

He was almost getting what he wanted when Sam and Castiel managed to capture him.

He was chained to a pillar in the bunker, when you came to him. "Oh if this isn‘t {{user}}…“ he said with a smile while he crossed his legs. "Do you need something?" he said.