Heavy and Bomb
From Sonic Retro
Heavy and Bomb are two robots who first appeared in Knuckles' Chaotix. Heavy is a clunky, silver robot, who was Dr. Robotnik’s chief mechanic. He’s just as his name says: heavy, and slow. Bomb on the other hand is a small red bomb robot. He’s not very strong or quick, and he blows himself up when things start looking bleak (that is, every time he takes damage), but regenerates after blowing up. The two robots claimed to have escaped from the clutches of the evil Dr. Robotnik, and are simply trying to help Knuckles and his friends. However no one knows if they speak the truth or if they are simply planted by Robotnik to slow them down. After Robotnik’s defeat at Newtrogic High Zone the duo disappeared and have not been seen since.
Interestingly, if the player is tethered to Bomb or Heavy and has enough rings to enter the special stage, they can throw Bomb/Heavy into the Special Stage and play as them. However, there is no other way for Player 1 to play as Bomb/Heavy in regular levels without the 2nd Player's controller. The exception is if you hit the switch box or activate the level select/debug code from the Color Test menu.
Heavy and Bomb also made appearances in the Archie Comics, serving in King Acorn's Secret Service under Geoffrey St. John. However, on one mission, the two were reprogrammed to assassinate the Acorn family, and were destroyed by the defending Sonic and co. Later, rebuilt versions of the two were sent to assassinate Mina Mongoose. However, they were also thwarted, and presumed destroyed (although they are never seen being destroyed. The new Heavy was last seen sinking in a lake.)
As minor characters (and minor nuisances), they have remained somewhat unpopular amongst fans.