The Robeasts are the monsters of the Drule Empire that they send to fight the two Voltrons of the Galaxy Alliance.
The robeasts from planet Doom were created through superscience and/or Haggar's magic, some of them simply being giant robots piloted by Doom soldiers or fully automated.
The Drule robeasts that battled the Explorer were uniformly technology based.
In Golion, they are referred to as Deathblack Beastmen and later Mechablack Beastmen. Dairugger XV called them Combat Machines.