The Hard Boiled Heavies were an elite squad of badniks created by Dr. Ivo "Eggman" Robotnik (Classic) in his quest to conquer the world.
At some point in the past, Dr. Eggman created the Hard Boiled Heavies to act as his elite Badniks. After a strange gem (the Phantom ruby) fell into Angel Island, Eggman sent the Heavies to investigate. Upon being exposed to gem's energy, they became more powerful and attempted to rebel against Dr. Eggman. Sonic eventually defeated them. Despite trying to usurp him, Eggman was not unswayed in using them again. 
Seasons of Chaos
Some time after their destruction, Dr. Eggman decided on reconstructing the Heavy King in order to provide his badniks with a commander. Not content with letting Robotnik be in charge of him, and after being prevented from eliminated the doctor by metal sonic, he overrode their loyal programming and took over Eggman's badniks. Using his new force, the HJeavy King promptly kicked Eggman and his Eggmobile out of his Winter Caverns zone base. Intent on using the Chaos emeralds to rule the world and to resurrect the rest of his squad as his generals, he tasked the badniks to search for the Chaos Emeralds.
Dr. Eggman's Birthday
Some time beforehand, Dr. Eggman went on to seemingly reconstruct the rest of the squad.
- The Hard Boiled Heavies first appeared in the game, Sonic Mania, which was set in the classic dimension of the Sonic the hedgehog game series.
- Out of all of the Hard Boiled Heavies, the Heavy Enforcer is the only member of the group that is absent in the stories.
- Sonic Mania