A CL4P-TP (You may call him by his locally designated name, Clap Trap!) is secreted away in Bloatfang's boss room (Act 3 - Some Assembly Required). After defeating the boss, step up onto the ledge where the Automaton Power Source and chest are waiting for you. There is a path you can follow that goes south and west around the boss arena. When you reach the southern point of the level you should see Clap Trap standing between a couple of rocks. He congratulates you for defeating Bloatfang, and then gives you a unique socketable to mark the occasion. (Claptrap's Bolt, rare socketable; Armor/Trinkets: Increase charge rate by 10%, Weapon: Conveys 5% chance to Shock for 5 seconds, Requires item level 32, "My servos... are seizing...")
Although you cannot interact with Claptrap, the interplanetary ninja assassin will continue to stand around and shout, as he is one to do. He has a number of lines of dialogue that are all parodies of his lines in Borderlands:
"Good as new! Welcome to... actually, I have no idea where we are!"
"Thank you stranger! Speaking of strange... you're either going to a costume party, or I'm a long way from home!"
"Look at me! I'm an easter egg! An easter egg!"