Rakkman is Named Enemy in Borderlands 2. He is located in the Fridge region on the Planet Pandora. You encounter him after completing the side quest “The Cold Shoulder” at the end of the Rat Maze at the Rakk Cave.
You can farm Rakkman for the Gunerang as he is the dedicated loot source for this item. Rakkman’s legendary item has a 10% drop chance.