Angels are spiritual servants of gods and demigods (usually Ennoc), made of pure light. They can manifest at the mortal plane to protect those they have formed a bond with, such as paladins. Usually they appear to mortal eyes as winged humanoids, but that is not their true form. Particularly strong angels can "touch" mortals and gain control over their souls as well as give them supernatural power, for example to fight for Ennoc without fear. People touched like that are referred to as Nephilim. The wizard-priests of Ennon were said to be Nephilim, and thus they were able to sink the whole continent of Mercution into the sea.
There are legends of dark angels who have "fallen from grace" and turned evil. This makes their power to turn people into Nephilim very dangerous. One such angel was Lucifuge, who is a sworn enemy of Heroica.