“Look out, everybody, things are about to get awesome!”
Proto Combat Loader are robots from Borderlands: The Pre-Sequel.
Proto Combat Loaders first appear at the very end of the Let's Build a Robot Army mission. They are produced by a Constructor, ex-Felicity Rampant. Being in red, and not to Jack's liking, the first batch gets scrapped. The second batch was in standard Hyperion yellow scheme. Subsequent fights with Felicity Rampant has her spawning these loaders, but only the red ones.
As Proto Combat Loaders do not spawn with a weapon, they are only capable of melee attacks. Being armored targets, explosive, corrosive and cryo weapons are the most effective against them.