Towards the end of the "Galactic civil war" there were reports of an unknown faction, clad in armour that resembled a mixture of the Republic's clone troopers and the Empire's stormtroopers. It is unknown at this time who they fought for as they vanished without a trace once their mysterious objectives were accomplished. On the rare occasion someone managed to take one of them out, their comrades would destroy any evidence, usually with a powerful thermal detonator, leaving nothing behind but a charred lump of armour and bone fragments. Investigations into their origins and motives are ongoing.
I couldn't find a decent reference for the helmet so I guessed half of it and just tried the to make the armour look more advanced than the clones and stormtroopers. It was "inked" and coloured at 3 in the morning after couple of days with no sleep but my colouring is shite anyway so nobody should notice