The servants of Darkness were corrupt versions of superpowered beings under the thrall of Darkseid operating in the future 31st century of the Legion of Super-Heroes. Their origins had changed depending of the different Legion continuity.
Great Darkness Saga
In the pre-crisis continuity, the Servants were clones animated and corrupted by the power of an amnesic Darkseid, to serve as his prime force until a full recovering of the dark god. The Servants stole several magic items from which Darkseid stole the power to feed himself. The overwhelming power of these servants was too much for the legionnaires and thanks to the intervention of the resurrected Izaya, the Legion could prevail.
This team of Servants included clones from: Superman, a Guardian of the Universe, Orion, Kalibak and Lydea Mallor (Shadow Lass' ancestor).
In the Post-zero hour continuity (earth-247), the Servants were differents: Instead being clones, a old, defeated Darkseid start using a time travel machine fueled by dark matter to travel to his younger self and steal his own power. The Servants were corrupted versions of heroes taken from the timestream and tortured and twisted in Apokolips until they fell under Darkseid control. However these paradoxes caused the timestream to start to collapse. When the Legion make the plan fail, the Servants were returned to their proper time without memory of those events.
This alternate team of Servants included doppelgangers of: a young Clark Kent, Firestorm, Big Barda, Green Lantern, Lobo and Orion.