The Megalo Legion is an army of mechanical monsters created by the Dragonia Kingdom for obstacles too powerful for just their armies such as the God Mazinger. Their appearance and role is similar to the Mechanical Beasts from the original Mazinger Z series.
While not much is given about them in the anime, in the manga they were originally powerful weapons that were used for a war on Dora. However, the battles and the great power these machines possessed destroyed the planet forcing the inhabitants to find a new planet. While they were kept in storage, Dorado had them banned from use due to the danger they represent. His son Eldo however released them in an attack on Mu. Before the Megalo Legion could do anything however, they were destroyed by an earthquake caused by the God Mazinger.