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.
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 leave, and he's been burned before. That doesn't stop the fangirls, though.
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.
Moses in the Bullrushes: As soon as Aku attacked their kingdom, his parents sent him out of the country on a lifelong training mission and was raised by various different mentors in different lands.
Mr. Fanservice: Oh so much. He's even got some fangirls in universe!
No Name Given: "Jack" is an alias he took in the future.
Named By Democracy: Its what the first people he talks to call him and they introduce him as Jack to their friends...then Jack is put up on his wanted posters...
One-Man Army: In the premier he takes down a whole army of killer robots by himself and wins, and in other episodes he routinely destroys multiple opponents at once.
Phil LaMarr: Yes, the same guy who got shot in the face in Pulp Fiction, was a cast member on Mad TV, was Static and Green Lantern John Stewart (among other roles) in the DCAU, and was a limbo-ing bureaucrat (among other roles) in Futurama also did this show. It takes a few episodes for him to pick up the Asian accent, but when he does it's spot-on.
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.
The Wise Prince: He's actually a prince, and the day Aku appeared signaled the end of his sheltered childhood.
Aku
Long ago, a single small fragment of an Eldritch Abomination fell to Earth. Given form, 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.
Bad Boss: You're probably safer as one of his victims than one of his minions.
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.
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.
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.
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 sparring 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.
Large Ham: So hammy that one of the first things he makes his slaves do is build statues of him.
Mako: His voice actor in one of his last and most memorable roles.
Meaningful Name: The word "aku" means "evil" in Japanese. It's also worth noting that he's the only major character in the series who is known by his real name.
Sealed Evil in a Can: Jack's father defeated him by sealing him away instead of killing him. The first episode shows him breaking free and taking his revenge.
Sizeshifter: A natural extension of his shape-shifting ability, and in his default form he's usually gigantic. He tends to shrink whenever Jack's sword hits him, though.
Voluntary Shapeshifting: He can transform into pretty much anything, and even introduces himself as a "shape-shifting master of darkness" during the opening narration.
Stupid Evil: He would actually have succeeded in defeating Jack many times over by now, if he could just resist throwing a Villain Ball at the most inopportune time, he abusesMooks, double crosses bargains or just spends too much time gleefully torturing Jack when he could easily crush him in an instant, all just before the job is done. Jack's survival, and to extent, he and his sword's very existance, is owed to this happening time and time again.
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.
Jerk with a Heart of Gold: He absolutely adores his wife, and if Jack is in trouble he won't hesitate to help.
John DiMaggio: His voice actor, who just might have came up with a bunch of his bizarrely colorful insults himself.
The Lancer: He's the closest thing Jack has to a best friend in this world.
Large Ham: He's the second most-wanted man on the planet and will brag about it endlessly.
Lightning Bruiser: Despite being three times the size of Jack, he can easily match the samurai's speed to the point of them ending their fight in a standstill....three days later.
Man in a Kilt: And it's definitely not for fanservice.
Nigh Invulnerability: When robot alligators bite his arms, he just laughs at them.
Like Cannot Cut Like: Jack's sword fails to break his thanks to it having similar magical properties.
Jack's Father
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.
Royals Who Actually Do Something: He's actually an emperor, but that doesn't stop him from charging into battle when his subjects are in danger. Now you know where Jack gets it from.
Posthumous Character: Except for certain episodes that take place in the past, he's long dead in the present timeline.
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.
