Heroes 6 - Discussion

Can anyone tell me, who exactly is the archangel Michael?

A great hero. A renowned angel commander.

I understand that he is on the side of Haven, but I suspect that in the end he will switch to Lucifer's side.

Firstly, there is no "Lucifer" here, unless one of the demon lords is given that name. Secondly, the traitor is Sarah, which is clearly visible in the very first video. No, it is not impossible that Michael's plans are not the most benevolent, but I don't think he will side with Urgash.