Even amongst yordles, Rumble was always the runt of the litter. As such, he was used to being bullied. In order to survive, he had to be scrappier and more resourceful than his peers. He developed a quick temper and a reputation for getting even, no matter who crossed him. This made him something of a loner, but he didn’t mind. He liked to tinker, preferring the company of gadgets, and he could usually be found rummaging through the junkyard. He showed great potential as a mechanic. His teachers recommended him for enrollment at the Yordle Academy of Science and Progress in Piltover, where he may very well have become one of Heimerdinger's esteemed protégés, but Rumble refused to go. He believed that Heimerdinger and his associates were "sellouts", trading superior yordle technology to humans for nothing more than a pat on the head while yordles remained the butt of their jokes.
When a group of human graduates from the Yordle Academy sailed to Bandle City to visit the place where their mentor was born and raised, Rumble couldn’t resist the temptation to see them face-to-face (so to speak). He only intended to get a good look at the humans, but four hours and several choice words later, he returned home bruised and bloodied with an earful about how he was an embarrassment to "enlightened" yordles like Heimerdinger. The next morning he left Bandle City without a word, and wasn’t seen again for months. When he returned, he was at the helm of a clanking, mechanized monstrosity. He marched it to the center of town amidst dumbfounded onlookers and there announced that he would join the League of Legends to show the world what yordle-tech was really capable of, without hiding behind a foreign banner.
"Ugh, it’s gonna take forever to scrape your face off my suit!"
Harpoon? Check. Flamethrower? Check. Triple rockets? Check, check, and check. Just to be safe, we’ll throw in one mischievous yordle whose mechanical prowess has been used to make the most diabolical machination ever to hit the Fields of Justice. Meet Rumble, the Mechanized Menace. His desire to see you burned, speared, crushed, stomped, blown up, or otherwise grievously injured, has him pushing his war machine way beyond what would be considered safe operating procedure, even if he might blow a gasket. But don’t call him short. That’ll really grind his gears.
Flamespitter: Rumble torches the area in front of him with his flamethrower dealing damage to all units in a cone for several seconds. While in the "Danger Zone," this spell deals additional damage.
Scrap Shield: Rumble creates a shield blocking incoming damage for several seconds and granting a short duration speed boost. While in the "Danger Zone," the shield's strength and speed boost increase.
Electro-Harpoon: Rumble launches a missile that deals magic damage and applies a stackable slow on the target. A second shot can be fired for no additional cost within several seconds. While in the "Danger Zone," the damage and slow percentage is increased.
The Equalizer (Ultimate): Rumble calls down a line of rockets over the target location. Enemies in the scorched area take damage over time and are slowed.
Junkyard Titan (Innate): Rumble's abilities generate heat. When Rumble is above 50 heat, he is in the "Danger Zone," causing all his basic spells to have additional effects. When Rumble reaches 100 heat he overheats, silencing himself and causing his physical attacks to deal additional magic damage. Rumble loses heat over time.