The Story of Rumble
Rumble is a yordle with something to prove and a mech suit to prove it with. He built Tristy — his mechanical battle suit — from salvaged Piltovan technology, choosing to work with scrap and ingenuity rather than accept the Hextech advantages that piltovan yordles have access to. This choice is ideological: Rumble is acutely aware of the gap between Bandle City's yordles who moved to Piltover and the ones who didn't, and he is not interested in closing that gap by becoming what he's distinguished from.
His technical skill is genuine — Tristy functions, which is more than most self-taught builders working from salvage can claim, and it functions in combat conditions, which is a harder standard. He is also extremely loud about his opinions on class, on the condescension of the technically privileged, and on the specific irritation of being underestimated by people with better equipment. He is right about most of this. He is not always diplomatic about being right.
He fights in Runeterra's conflicts not with Bandle City's backing or Piltover's endorsement but on his own terms, in Tristy, fueled by the specific energy of someone who has decided that proving capability matters more than the circumstances that made it difficult. He is very good at what he does. He wants people to know this. He is working on the balance between those two facts.