Cygnus, referred to as "the Old Man" by his apprentice, is a non-playable character in Orcs Must Die! and Orcs Must Die! 2. He narrates the main story during cut scenes and appears in dialogues between characters in Orcs Must Die! 2.
He is the oldest War Mage in The Order, having fought for it for 300 years. He was also the teacher of both The War Mage and The Sorceress. The Sorceress was his first apprentice and he taught her everything he knew. (so good in fact that she decided she should rule) When she left the Order to use Horde against the Order the Master felt responsible for her actions and as such he neglected the education of his second apprentice, the War Mage. Especially because the War Mage wasn't the brightest mind (or just plain idiot) in the Order and was deemed simply unteachable in the magical arts.
Prior to events of Orcs Must Die! he was one of the last War Mages defending Rifts from the Orcs. He fought against endless hordes only to one day slip on the blood of a kobold and supposedly crack his head on the portal stairs themselves. Left for dead, the War Mage took his crossbow and bladestaff and left him there; he didn't even check to see if his teacher was still breathing. The Master was left unconscious, but he watched the War Mage's progress telepathically and was quite amused that there was actual progress, apparently his worst and stupidest apprentice didn't die defending the Rifts but rather surprisingly prospered even when the other War Mages perished.
The Master regained consciousness shortly after the War Mage closed the last Rift and sealed the magic flow between two worlds, which in effect foiled the Sorceress' plans. It was him who saved his first exiled apprentice from the orcs by opening a new Rift.
He knew that Rifts are responsible not only for the orc menace, but also all good advantages given by magic. The common people started starving without magical rains for growing food or dying from diseases when the healing magic failed.
He did say that of all the war mages, only his apprentice was determined enough to sacrifice even his own power by cutting off the flow of magic, or it was just plain stubborn stupidity.
That's why he decided to choose the "lesser" evil - the orcs, and began to construct new fortresses to contain new Rifts which restored the magic flow between worlds, while his two apprentices did what they do best - killed the orcs.
Thanks to their efforts, the magic returned to the world and the grateful people started joining the Order, and soon enough it was rebuilt under the guidance of the War Mage and the Sorceress.
After the magic returned, the War Mage and the Sorceress never saw their master again; he probably decided his time was over.