Because a plumber's Girl Friend was kidnapped by a Gorilla loose in the city. Armed with nothing but a shirt on his back, overalls, worker's boots and a mustache the brave plumber chased the Gorilla through the streets to the sight of an building under construction.
The Ape showed his superior strength, breaking the beams as he jumped up and down in the structure, but the plumber was not intimidated. The Gorilla through barrels as the plumber climbed after him, but the man would not slow down. The Ape then used and unexpected tactic voodoo magic he picked up from God knows where to make oil fires come to life and aid him but the plumber found a workman's hammer and beat back the flames, he smashed the barrels.
The desperate Ape fled, three times that very night the Gorilla would climb high objects, girl in tow, to escape the plumber's fury, but the righteous prevailed and the Ape was defeated.
And would you believe the chick left the plumber after all that? In a rage the plumber took out his anger on the Ape, capturing and torturing the animal but he was beat back to his senses by the Gorilla's son(who grew into the modern day Donkey Kong)
But it wasn't over. From an unknown location, strange creatures invaded to sewer systems of Modern Plumbing. The plumber and his brother ventured into the depths to destroy these monsters so that people could once again flush their toilets in peace. They battled for what seemed like an eternity and ended up in a world called the mushroom kingdom.
After getting over the loss of everything he knew(besides his useless brother) the Plumber once again setup shot and went to work fixing pipes. Somehow he got on the badside of a Giant Dragon-Turtle who ruled over a Kingdom far away from the Mushroom Kingdom.
Little did the plumber know that as a baby he had accidentally fell off the wings of a stork and landed on an Island on the coast of the Mushroom Kingdom. The Island was home to a dinosaur herd who had hostile relations with the Turtle Kingdom. The Turtle king employed mercenaries to destroy the baby who the Dinos had found but they succeeded in fighting the paid hands off and returning the baby back home.
The Turtle still remembered though the plumber did not. The Plumber became known as the best in the business and even had the pleasure of working for the King, and came to know the Princess Quite well, but the Turtle saw opportunity. His forces stormed the Mushroom Kingdom and attacked the Mushroom Kingdom, taking the Princess Knowing the plumber would follow right into their traps.
But the plumber beat the odds and made it to the Mighty fire-breathing beast's Castle. The Security was no match for him and he met the leader in fierce combat. The Plumber found the Turtle's shell unbreakable, and his flames unbearable but he found an Ax and out whited the beast, cutting a rope bridge and plunging the Turtle King into liquid hot magma.
The Princess was saved, but their was no happy ending, for the Turtle King survived the lava and has since been a thorn in the plumber's side. It wasn't all bad though, the useless brother did eventually get a backbone and inherited a large Mansion. The plumber briefly owned a castle, until it was smashed by a brute with Herculean strength and now lives in modest shack.
