Was the Biblical Angel of Death good or bad?

Hi, I'm wondering what everyone thinks about this. The Angel of Death killed the Egyptians' first-born sons, and recently I also read that God let the Angel of Death kill the Assyrians (Sennacherib's army). Is the Angel of Death an angel in league with God? Or is it actually a demon that God gave permission to kill and sow death? Is there anything in the CCC or Church teaching that talks about this?