You will not find pizza parties or exploding "Cowabunga!" word bubbles in the original Teenage Mutant Ninja Turtles comic. Instead, the Turtles' early adventures are loaded with swearing and extreme violence.
The first appearance of the Teenage Mutant Ninja Turtles came in 1983 when a mutated rat sent his adopted mutant turtles on a vengeful killing rampage to take down the Shredder, who they successfully slew before moving on to bigger and badder foes.
These days, the Heroes in a Half Shell are ubiquitous - as are a slew of TMNT ripoffs - but younger fans may be surprised to learn the crew's dark origins. While the concept has always been a little goofy, the hilarious jokes and good-natured comradery are newer additions to the franchise.
Splinter becomes a displaced rat because his owner, Hamato Yoshi, is killed by another ninja named Oroku Saki, AKA the Shredder of the Foot Clan. This loss instills a desire for revenge in Splinter, and he uses the Turtles to bring his plot to fruition. He adopts and raises the Teenage Mutant Ninja Turtles, but he is not so much a loving father as a puppeteer, molding his apprentices into killing machines. They are weapons - Splinter's tools, not his children.
While Shredder's machinations in the cartoons and movies usually amount to vague criminal activity that often involves scheming against the Turtles, he wasn't always a generic cliche.
In the comics, it's quite clear how his organization amasses its wealth: through drug and arms dealing. Shredder doesn't found the Foot Clan, but instead rises through the ranks after proving his ruthlessness. Like the Turtles, Shredder is also a hardened killer, and Mirage Studios makes no effort to downplay his bloody history.
In the animated series, Shredder uses a pizza shop as a front for his undefined criminal activities - definitely less menacing.
When Casey Jones is introduced in the original run of comic books, he's an unhinged guy who just wants to beat criminals to death, regardless of the severity of their transgressions. Not only does Casey use his signature hockey stick to dispatch wrongdoers, he's also down to brutally beat people with baseball bats.
He first meets the Turtles after Raphael stops him from killing a group of muggers. While his violent streak calms down a little after that, he does end up killing a teenage mugger and falls into an alcohol-fueled depression as a result.
In the beginning, Shredder isn't the Turtles' main antagonist, as he's killed off in the first story arc. In a back-and-forth rooftop battle, Leonardo takes down Shredder by plunging his sword right through the villain.
With Shredder brought to his knees, the Turtles offer him the chance to commit seppuku (ritualistic suicide practiced by historical Japanese warriors defeated in battle). Instead, Shredder pulls a dastardly move and whips out a grenade, but Donatello quickly knocks him off the roof to his death.
Of course, the Turtles don't stop at killing Shredder. The brutal reptiles also dispatch countless members of the Foot Clan from this world without a second thought.