Piston is an NPC in Borderlands 2
He is part of the Mister Torgue's Campaign of Carnage DLC
Piston is considered the number one gladiator, the best warrior in the tournament. He is willing to sponsor you in the Arena. You need a sponsor to progress through the ranks. Piston is interested in working with you to help you get into the tournament and move you forward through it.
"Piston's talking to you, baby. I'm impressed with how you're handling yourself out there, Vault Hunter. I hear you need a sponsor, and as it so happens, I need a new apprentice. Come find me at the arena. Just follow the scent of success"
Interviewer: Piston, what would you say to those who accused you of cheating - of rigging fights to gain your number one ranking?
Piston: Oh Jefferey. Well I guess I'd say I have to do this... and then I tell them to NEVER! CALL! ME! A! CHEATER!. And you can quote me on that.
"Here's what Piston is offering, chickadee - Piston will sponsor you. Piston will take you under his muscly wing and we will open that Vault together. I've already set up your first fight in the arena. Get in there and show'em that Piston and the Vault Hunter are a force to be reckoned with."