Nobody knows The Commander's real name except for High Prefect Apateon himself; they simply know his reputation. He is a career soldier; having fought firstly for the army of Brytton in the endless territorial disputes which followed The Fall, and then as a mercenary when he was dishonourably discharged.
At some point in that career, he came to the attention of a certain ambitious member of The Council and was recruited to act as a Special Operative (or assassin) on his behalf. The Commander rapidly built the man then known as Ataraxias a highly trained - and lowly principled - private army. The Commander is directly responsible for Apateon's rise to power as he has trained every Keeper and soldier employed by the Union or, at least trained those they learned from.
Under the streets of Lundun, he lost his best unit to the spear of a the Dracograth Neshaa in the then-empty Dragon's Nest. He was allowed to live in order to serve as messenger of Neshaa's ire.
Cap in hand and shamed, he returned to deliver the message and was suitably punished. Dozens had already died painfully under the care of Project Prometheus' doctors; either he would die and pay his debt or make himself useful, it was decided.
The Commander lived, much to the surprise of of everyone. He not only lived but he thrived; becoming stronger, better, faster. Oddly, The Commander grew no taller and exhibited only minor muscle growth, he even kept his facial scars. This was not known to be odd at the time but he retained his normal height while later members of Prometheus Company grew massively.
The Commander, with his suit of custom armour and decades of brutal experience, is not going to let that slow him down, even the giant Promethians fear him.