Claptrap's New Robot Revolution
This particular Claptrap serves as the final boss of the Claptrap's New Robot Revolution DLC for Borderlands, and because it is set after all the other story segments, the true final boss of Borderlands. The Interplanetary Ninja Assassin Claptrap was sent by the Hyperion Corporation as part of a new strategy to indirectly deal with Roland, Lilith, Mordecai, and Brick, the Vault Hunters who'd been a thorn in the side of Hyperion throughout the Borderlands campaign. Since all attempts by anyone to kill the Vault Hunters through direct frontal assault had ended in failure, "INAC" would lay traps, poison food supplies, and spread rumours about the Hunters to get all of Pandora to turn against them. Unfortunately, INAC was made extra-intelligent in order to accomplish these tasks, and he used this intelligence to override his programming, whereupon he set out to accomplish galactic domination, reprogramming the Claptraps of Pandora to serve him as footsoldiers, as well as forcibly transforming a wide variety of organic creatures into partially robotic slaves, including Skags, Rakks, and Spiderants, and even intelligent creatures like Bandits, Crimson Lance soldiers, and the late General Knoxx.
Ultimately, the Hunters confront INAC at the bus stop from the very beginning of Borderlands, whereupon he summons an enormous battle tank he calls "MINAC" - the Mega Interplanetary Ninja Assassin Claptrap - and directly engages the players. Upon MINAC's defeat, INAC pops out and puts up minimal resistance as the Hunters blow him away, using a device on him once he's disabled to reset his programming to basic Claptrap standards and transforming him into the harmless dancing Claptrap on the game's main menu.
Borderlands: The Pre-Sequel
In this game, taking place between the events of Borderlands and Borderlands 2, the specific robot who was once the Interplanetary Ninja Assassin Claptrap is taken by Jack, a low-level programmer for the Hyperion Corporation who would one day become Handsome Jack, the tyrant of Pandora, and reprogrammed into a direct combat role, inspired by the very team of Vault Hunters who defeated INAC. With this glitchy, questionably legal software installed, Claptrap is renamed "FR4G-TP", or "Fragtrap", and added to a group of Vault Hunters hired by Jack - Athena, Nisha, and Wilhelm - to help him search for a hidden Vault on Elpis, the moon of Pandora.
Fragtrap's active skill, Vault_Hunter.exe, is meant to analyze the combat situation and intelligently deploy a skill based on an existing Vault Hunter, such as deploying a miniature Claptrap that fires missiles and bullets in a recreation of Axton the Commando's combat turret, or summoning a murderous axe and vastly increasing his physical strength, in the manner of Krieg the Bandit Psycho. However, because it's still in beta - and technically classified as malware - in reality, the program merely selects one of these abilities at random, as well as selecting from a number of much stranger abilities not based on anything specifically, like deploying sails and black powder cannons to turn Fragtrap into a pirate ship, and glitchy negative effects, like making Fragtrap and all his party members uncontrollably bouncy.