They are armored battle robots built by David Xanatos, their abilities and appearance modeled after gargoyles in general and Goliath specifically. Xanatos also wears a battle armor suit, modeled after the Steel Clan (distinguishable by its red and black trim), that he frequently wears when he needs to do things beyond his normal physical capabilities, especially when battling Goliath and the gargoyles.
The Steel Clan robots possess rockets on their backs along with stabilizers on their feet which allow flight, and razor-sharp wings for maneuverability. They are equipped with retractable arm-cannons on their right forearms, along with razor-sharp talons. The second batch onwards were capable of discharging electricity along their bodies to prevent enemies from coming into physical contact with them. Their programming is still primitive, as they continue to make similar mistakes, such as flying into buildings and each other.
When billionaire David Xanatos learned of the existence of gargoyles, he immediately saw them as a potential resource that could be used. He attempted to manipulate and/or coerce Goliath and the Manhattan Clan to serve him as a veritable personal army, though he soon realized that Goliath was not going to be as subservient as he had hoped. Having anticipated this, however, Xanatos put secondary plans into motion. Using information (which the gargoyles had unwittingly stolen for him), he activated the Steel Clan, which was designed by Xanatos specifically to replace Goliath's clan as Xanatos' muscle.
These robots resemble Goliath in general appearance and size. Unlike gargoyles, which can only glide on wind currents in the manner of gliders, the Steel Clan robots are equipped with rocket engines, giving them the power of controlled flight. They are also armed with a beam weapon that is built into the forearms, and have computerized control systems that links them to a command interface in Xanatos' own gargoyle-like battle armor.
Over time, several versions of the Steel Clan were created. The original version, first seen shortly after the gargoyles awoke in Manhattan, and an apparently improved version later used when Xanatos used one of his robots to steal the Eye of Odin, were similar in design and function. Parts of a Steel Clan robot were joined to the stone remains of Goliath's dead rookery brother to create Coldstone, and two similar but redesigned robots were later constructed to host the spirits of two other rookery siblings (dubbed Coldfire and Coldsteel).
A third and radically-redesigned version was also created by Owen Burnett called the Iron Clan.