When General Edward Riesen accepted Julian's offer to cure him of his heart disease, the disembodied higher angel Duma was pulled from The Ether and entered into his body, combining their spirits and making them into a Dyad.
At first General Riesen's spirit was dominant, making the Dyad's agenda more specific to him. However, wanting him to lead his new eight-ball army, Gabriel needed to make Duma the dominant spirit. He did this by killing Clementine, the one who was keeping Edward dominant, which crushed his will, allowing Duma to rise above him.
He is currently leading Gabriel's eight-ball army, which was handed to him when he defeated another dyad, Julian. Duma's spirit is so dominant that Edward has little to no control at all, making it more of a possession.
Duma, combined with Edward, both have the personality of a stone cold warrior. This Dyad-combo of both men with battle and soldier experience brings a hard fight against those who oppose them.