Our hero, a samurai and the son of the samurai who initially released (and then defeated) Aku. He trained in every country in the world in preparation for the final battle... only to be hurled into the future before he could land the killing blow. Now he must Walk the Earth, seeking a way back to the past to finish that battle... not that this will stop him from setting things right in the future as well.
Blood-Splattered Warrior: Well, it's oil instead of blood, but Jack regardless blatantly and commonly gets the same concept applied to him in his battles with a color change to be PG.
Celibate Hero: He's got at least four valid motives for avoiding romance; it would distract him from his quest, he's a danger magnet, he'd have to return to the past, and he's been burned before. That doesn't stop the fangirls, though.
The Chosen One: Unbeknownst to him, he's going to be this when he's older.
Katanas Are Just Better: Of course, the only reason being it was forged by the gods from his father's righteousness. It appears to be evenly matched with The Scotsman's sword, which was similarly mystically enchanted.
Nice Hat: Sometimes wears one made of straw. Episode 26 reveals that he knows how to hand-weave a hat from the husks of straw, which explains how he always manages to procure replacement hats when they get continually pulverized.
The pilot had him wearing a kabuto helmet made from scrap metal as part of a set of improvised armor.
When Jack tells Ikra (who, as Aku, is almost the only being in the future that could know Jack's name) that he is called Jack, her expression is priceless. Of course, had she accidentally let slip his real name, she would have blown her cover right then and there.
The Quiet One: Usually speaks only a few lines each episode; some episodes he never speaks at all.
Tyke Bomb: Non-evil example; Jack began training with numerous combat styles and many different warriors as a child, after he and his mother fled Aku's second attack on their homeland. Unlike most other examples, he was still brought up as a benevolent samurai with a code of ethics.
Flashbacks scattered thorough the series' run show that despite the rigorous training, Jack made many friends in the different countries he visited, played, and learned with the different people and cultures he met. Some people should take notes from this series on how to properly raise a One-Man Army.
Long ago - very long ago - a single small fragment of an Eldritch Abomination fell to Earth, wiping out the large saurian creatures that dominated the planet at that time. It existed as a mindless evil for millions of years until a brave king attempted to destroy it: the attempt to destroy it instead gave it consciousness. It became Aku, a being of pure darkness and evil. When the samurai who would later be called Jack came to fight him, Aku hurled him into the future as a last-ditch effort to survive. In the future, Aku rules the world, and devotes a lot of effort to finishing Jack once and for all.
Card-Carrying Villain: Often refers to himself by several evil-sounding titles, just in case you couldn't tell he was evil by looking at him.
Combat Tentacles: Whenever he's in octopus form (one of his favorites) or reverts to formlessness.
Complete Immortality: He hasn't aged at all since the day he was 'born' and heals from injuries almost instantly. The only weapon that causes him real harm and could potentially kill him is Jack's sword.
Immortality aside, the episode "Jack and the Gangsters" shows it is still possible to at least overpower him and keep him at bay. The episode revolves around a MacGuffin called the Jewel of Neptune, a powerful artifact that even Aku himself is unable to seize due to the powerful elemental spirits guarding it. His numerous attempts to steal it have resulted in him getting his ass handed to him, and during the timeframe of the episode, he'd long since given up trying. Cue Jack infiltrating a group of Aku-friendly mobsters and obtaining the jewel so he can be granted the opportunity to meet Aku face-to-face.
Dark Is Evil: In addition to being mostly black, his primal form is nothing but a billowing dark mass.
Evil Cannot Comprehend Good: A large reason that his attempt to throw Jack into the future backfired. He'd expected a world ruled by him would allow him to crush Jack effortlessly when he arrived. He never took into account that a hero arriving and successfully fighting back his forces would trigger Hope Springs Eternal and start giving the oppressed masses someone to rally behind. Also shows when he tries to make himself out as the good guy in the stories he tells to children in one episode, one of the prime reasons it doesn't work is he didn't really comprehend what being The Hero actually meant.
For the Evulz: The only real explanation for his actions: Aku does what he does because the suffering of others amuses him, as demonstrated by his signature Evil Laugh.
Jerkass: Fairly obvious as he is a villain, though he tends to swing back and forth between a comedic villain and truly evil one. Notable acts of evil include in the pilot episode when some aliens that lived an aquatic world whose oceans were dried up come to him requesting to live on Earth and reveals that he dried up their planet, though he does let them stay on Earth provided they build statues every month. Another note is when he forces a scientist to build a set super robots to kill Jack under the promise of sparing his village if does, and then tests the robots out by having them burn his village to the ground and kill everything in it.
Laughably Evil: He's rather... Goofy for being the Ultimate Evil and all.
Varies depending on the episode, there are some that present him as legitimately evil and threatening figure. Or sometimes a bit of both.
Narcissist: He once said "No mortal can defeat him." right before getting his ass handed to him, asked for a group of fish people to build statues of him every month, and sees Jack as foolish for even trying to fight him.
Aku's last resort to send Jack into the future as Jack was about to off him. If Aku can open a portal in time in this situation, surely he was strong enough to do something a little more fatal than that. Sure, Jack's stuck in the future, but fact is that he is still alive.
A large, extremely loud Scottish man, with a sword inscribed with magic runes and a machine-gun false leg. He's about as burly a warrior as you'll find, and one of the few creatures able to match Jack for combat prowess. One of the few characters who appears more than once in the series.
Noodle Incident: Why the Scotsman is the second most wanted person in the world, presumably for Aku, is never said. However, it can be assumed that he similarly resists Aku's rule, and his ability to hurt Aku and power similar to Jack would support that.
No Sell: In "Scotsman Saves Jack Part II", an amnesic Jack, the Scotsman, and a bunch of pirates sail the ocean, only to come within range of the song of Enthralling Sirens. Everyone on the ship becomes hypnotized, except the Scotsman. Why? The fact is that the song of the siren enchants men due to how beautiful it is to their ears. The Scotman thinks their singing is horrible.
Like Cannot Cut Like: Jack's sword fails to break his thanks to it having similar magical properties.
Voiced by: Sab Shimono
The samurai lord who accidently awakened Aku when he tried to destroy the corruption he was otherwise unconsciously causing. The gods Odin, Ra and Vishnu forged the sword that would later become Jack's from his righteousness. He manages to seal Aku, until he returns once again to unleash evil. Apart from the first episode and the two-parter covering him awaking and sealing Aku, he mostly appears in flashbacks.
Annoying Arrows: Clearly disregards having been struck by some arrows during his fight with Aku.
A retired, obsolete, prototype assassin android with emotions. He was blackmailed into targeting Jack, by Aku. Aku's leverage, he had kidnapped the one thing dear in the robot's life: His precious dog LuLu....sweet thing.
Just a Machine: Possibly averted due to Jack's reaction after X9 muttered his dying words.
Killed Off for Real: Inevitably, after a tension-filled confrontation, Jack catches X9 while his back is turned and runs him through. Because X9 refused to back down for the sake of Lulu, Jack had no choice but to finish off X9 before the robot did the same to him. X9's final request was for Jack to find his precious Lulu and take care of her before he went offline for good.
A powerful warrior that guards a time portal, waiting for The Chosen One to find and use it. When Jack finds the portal, he is told by the Guardian that he's not the one, leading Jack to try and beat him anyway.