Aku

"Long ago in a distant land, I, Aku, the shapeshifting Master of Darkness, unleashed an unspeakable evil! But a foolish Samurai warrior, wielding a magic sword, stepped forth to oppose me. Before the final blow was struck, I tore open a portal in time and flung him into the future, where my evil is law! Now the fool seeks to return to the past, and undo the future that is Aku!"

- Aku during the opening sequence of Samurai Jack.

Aku is the main antagonist of the Samurai Jack series. He is a ruthless, diabolical, and manipulative demon who is the archenemy of Samurai Jack. He is easily one of the most successful cartoon villains, as he managed to rule the world, and has been unstoppable for years. It is also later implied that he is actually created by a black virus that is the true ultimate evil.

Aku tends to switch back and forth between being played for laughs, and being a truly threatening villain. He would either do something pettily "villainous" not to be taken too seriously, like telling stories to children to make them like him instead of Jack, or be extremely unsympathetic, like causing genocide and enslaving innocents, depending on the episode.

He was voiced by the late legendary Japanese actor Mako Iwamatsu, who also voiced Happy Cat in Duck Dodgers. He is currently voiced by Greg Baldwin in the fifth and final season.

History
Originating long ago in the depths of space as a formless evil Aku was banished by the gods Odin, Ra, and Vishnu in order to protect the universe from his influence - yet a small shard of the great shadow managed to survive and flew off into space - for many years this shard continued flying through space until it eventually landed on Earth, causing the extinction of the dinosaurs in the process.

Many years later, the site on which Aku landed would become the ancient island of Japan, which Aku infected like a horrible disease - creating vast forests of evil in the land and threatening to consume it, eventually Aku's threat became so great and impressive that Jack's father decided to rid the land of the demon once and for all using magical-oil made by Buddhist monks, however, when he fired an arrow coated with this oil into the evil entity it didn't destroy it but rather gave it form and sentience, thus forming Aku as a humanoid threat of just unimaginable power.

However, with aid from Odin, Ra, and Vishnu Jack's father created a magical sword powerful enough to defeat Aku and fought the demon, at the end of the conflict Aku was transformed into a tree - yet the imprisonment wouldn't last much more than a decade before a solar eclipse freed Aku again.

Aku would then proceed to lay waste to the kingdom Jack's father ruled and engaged in a battle with Jack himself - Jack very nearly killed Aku for good using the magical sword but Aku threw open a portal in time and transported Jack to a future-world in which Aku ruled supreme.

For the rest of the series, Aku is portrayed as the tyrannical, omnipresent, all-powerful, and manipulative ruler of the world and is an almost unstoppable force - yet he fears Jack, knowing very well that the warrior has the power to slay him, Aku has placed a high bounty on Jack's head and is always trying to dispose of him, whether it be with manipulation, cunning, force, or trickery.

Samurai Jack (2017)
Aku returns in the new season and will fight against Jack for the last time, possibly meaning that he will be defeated by Jack and will be destroyed forever. In the series, it is also shown that Aku has no association with the Cult of Aku and likely has no idea that it or it's followers exist.

In the first episode, Jack fights an assassin named Scaramouche who claims to be "Aku's favorite assassin".

In episode XCIII, Aku wakes up from his long nap and becomes annoyed with his Royal subjects and minions as they come to his lair, bow down to him and give him gifts while he is trying to do his daily routine. When his minions mention that they built more robots to destroy Jack, Aku states that he doesn't care anymore. Aku then creates a clone of himself to serve as a psychiatrist who asks him about what has been troubling him lately. Aku tell the psychiatrist that it's been 50 years since he destroyed all the time portals and that he hoped that Jack would've just died off the normal way, but, as a result of the time traveling process, not only has Jack not died from old age but he hasn't even aged a single day and has become biologically immortal, deeply frustrating him.

In Episode XCVI, Aku, after being informed by a henchman that the former's lair was under attack by an army lead by the Scotsman, decides to deal with them himself and flew out of his lair. Later, he shape-shifts into a colossal giant ball and effortlessly slaughtered most of the army. After this, he was confronted by the Scotsman, with the latter insulting and ridiculing Aku, stating that Samurai Jack inspired many to oppose him. However, this leads to Aku killing the Scotsman by shooting him with his eye beams. Aku, with a bored tone, only wondered why the Scotsman brought up Jack before returning to his lair. However, unknown to Aku, the Scotsman returns as a ghost and instructs his army (who are all his daughters as well) to continue to amass their forces and find Samurai Jack.

In Episode XCVII, Scaramouche (now only a head) tries to reach Aku in order to tell him that Jack is missing his sword and calls him from a phone booth on the boat he was riding, although Aku immediately hangs up after Scaramouche is thrown off the boat.

In Episode XCVIII, in a flashback, it is shown that Aku pulled Jack out of a time portal just as he was about to reach the past and then obliterated it, taunting Jack by telling him that said time portal was the last in existence. In his rage, Jack tried to destroy Aku once and for all, although Aku backed out of the fight and transformed the Rams that had been helping Jack into mindless beasts that he soon killed, causing him to accidentally drop his sword into a pit in his horror.

In Episode CI, he will meet his ultimate fate.

Personality
"That sword, I remember that blade, I recognize your blood. You are the son of the fool who imprisoned me those many years ago. No matter, neither he nor the sword had the power to slay me forever, and neither do you!"

- Aku meeting Jack for the first time.

Aku is evil incarnate; he embodies the very essence of an evil overlord. Cruel, uncaring, omnipotent, domineering, and authoritative to all he meets, it is obeyed or obliterated with Aku. He is truly selfish, cunning, arrogant, deceitful, oppressive, temperamental, uncontrollable, destructive, egocentric, and sadistic by default, so he has ruled the planet for thousands of years and does not take kindly to disobedience. An example of his cruelty can be shown when an alien prince and princess had crash landed on the Earth and begged for his help because they needed to get back to their planet to stop an invasion; Aku had their ship confiscated and ordered them thrown into a forced labor mine where they would live "miserably ever after" while laughing about it. When their robot companion objected to this treatment, Aku smashed him into the ground without hesitation. The same episode also showed a dog in his castle being tormented by electrocution and whipping for unknown reasons. Although he is extremely treacherous, bloodthirsty, unpleasant, merciless, and inhumane, to say the least, he has enough of an understanding of humanity to manipulate their feelings to his advantage.

Aku is as intelligent as he is powerful, and his cunning knows little end, from taking the form of a woman to trick Jack or manipulating various races into serving him. He is also extremely dishonest, traitorous, and manipulative, so he has no shame or remorse, and he routinely goes back on his word either to serve himself or simply for amusement.

Despite this, he possesses a dry sense of humor and often jokes when in a good mood, mocking Jack whenever he can and however he can. For instance, in one episode Aku holds a time portal just out of Jack's reach as Jack jumps for it.

He is also rather "genre savvy", and will occasionally lean on the fourth wall or lampshade either his own villainous tendencies or various cliche situations.

He is also a frequent, pervasive, and ubiquitous source of comic relief in the show, due (in prime) to his reactions to the things around him.

While Aku seems to have a soft spot for children at times, this seems to be mostly indicative of his views of seeing immense value in not simply eradicating them, but rather convincing them via various means to view him as the "hero" of the planet and not Samurai Jack, making them useful servants in the future to shape successive generations. This can be seen in Aku's Fairy Tales where he attempted to make children admire him by telling them tales that depict himself as a hero and Jack as a villain. Unfortunately for him, the children weren't impressed hearing his increasingly ludicrous tales, causing him to vanish in rage after roaring "the end". In Jack and the Rave, he composed an evil techno music that hypnotizes children, again showcasing his lust to indoctrinate young kids into his evil ways, making them dance for him and commit crimes. Despite this, Aku's many genocides of countless nations have included children as well and the villain previously targeted a young Samurai Jack shortly after the subjugation of his homeland, knowing the threat the son of his former nemesis, the Emperor, would pose to him if left unchecked.

After 50 years during his fight with Samurai Jack, Aku became upset, depressed and no longer sees Samurai Jack as serious threat anymore. Due to the side-effects of time travel, Samurai Jack hasn't aged and cannot die even by effects of old age. He has no interest to fight Jack and wish someone else to just kill him.

Powers and Abilities
Aku is a powerful demonic entity. He possesses a wide range and knowledge of demonic magical powers, that varies from episode to episode as the series demands. His powers, as shown thus far in the series include:
 * Shapeshifting: Called the "Shapeshifting Master of Darkness" at the opening of each episode, Aku can change into virtually any form that he desires, from a giant dragon to a small insect, or even a beautiful woman. He can also change his size, liquify himself, stretch, and expand his body. Aku's consciousness can exist even in a part of himself. He typically changes into animal forms that are threatening to fit certain situations, such as a scorpion or an octopus.
 * Near-immortality: As a demonic entity, Aku is ageless and nearly immortal. Aku's body is immune to nearly all forms of physical injury. Aku doesn't need to have food, drink, or air and is capable of interstellar travel.
 * Scrying: He also has the ability to spy on Jack through a large sphere he can summon at will in his tower.
 * Regeneration: He has immense regenerative abilities. Severe wounds regenerate in mere seconds.
 * Superhuman Strength: When Aku challenged Jack to a so called final match he was shown to have superhuman strength, even in a somewhat human form.
 * High-invulnerability: Aku has shown the ability easily withstand weapons of any sort, such as simply absorbing arrows shot at him or not even being fazed after being hit by torpedoes as well as being capable of breathing underwater and existing in the depths of space, however he was shown to be vulnerable against mystic weapons and the weapons and artifacts of Deities and especially Jack's blade which was forged through the very essence of purity within Jack's father by the Deities Odin, Ra, and Vishnu.
 * Fire Generation: Along with being capable of breathing fire Aku has also been shown creating it such as in one comical situation he had to re-ignite his eyebrows.
 * Time Travel: This was the very ability that Aku had used to send Jack into the future at the beginning of the series, though so far it has only been used once and was a one way portal forward in time.
 * Laser Eye Beams: Aku used this ability in numerous battles with Jack and he also used it to destroy the majority of Jack's Kingdom.
 * Teleportation: Aku uses this quite often to appear before those he has business with, such as the Imakandi.
 * Summoning Storms: Aku is capable of conjuring storms through will.
 * Conjuration: The ability to create objects out of thin air. He once used this ability to conjure gold, jewels, and treasure for the Imakandi.
 * Psychokinesis: Aku has shown the ability to move objects with his mind alone.
 * Sonic Scream: Aku was shown capable of producing a powerful scream that causes massive damage to the landscape.
 * Necromancy: Aku has been shown in one episode to be capable of animating countless dead bodies, and bending them to his will as they have neither mind nor soul.
 * Premonitions: On one occasion, Aku had a dream that Jack found a way to return to the past, and realized it was no dream but a premonition, which spurred him into successfully preventing it from happening.

Weaknesses
Despite his immense proficiency in dark magics and sorcery, Aku has some weaknesses. These include:
 * Shape-shifting Limitations: Regardless of the form he takes, Aku appears to be limited to the specific color scheme of red, green, and black. Furthermore, if his reflection is seen, it will always reveal his normal form regardless of the guise that he takes. This is most noticeable when Aku takes the guise of a hermit, and accompanies Jack to look for the artifacts of the gods. When Jack and Aku are in the swamp, Aku's normal form was apparent in the water's reflection even while in his hermit guise, so he splashed the water and used the ripples to hide his reflection.
 * Divine Magic & Artifacts: He can be harmed and subdued by any object or form of magic wielded by the gods Odin, Ra, and Vishnu. This also includes weapons forged using divine energy or essence, such as the Emperor's (and later Jack's) Samurai Sword.
 * Infectious Disease: In one episode (XLIII), he appears to have contracted a form of illness not unlike the human flu or common cold. Whether or not this was the result of a conventional infection, or the product of some supernatural equivalent, remains unknown.

Quotes
"I WILL RETURN!!"

- Aku

Trivia

 * Aku's name means "evil" in Japanese. The kanji is written as "悪", which can also be pronounced as "Waru".
 * Aku may also be named after, an evil spirit in Japanese folklore who is said to bring misfortune upon those who see it.
 * Aku has several similar villains worth noting:
 * Grandfather (Codename: Kids Next Door) - They are omni-potential black demons with similar powers, including brainwashing. They also both succeeded in ruling the world, but were defeated by the protagonist's father, and then came back and succeeded in ruling it again. Also, Grandfather and his son Father's designs are extremely similar to Aku's.
 * Dr. Ivo Eggman Robotnik (Sonic the Hedgehog) - They're megalomaniacs and evil geniuses, but are also extremely goofy and hammy, and aren't very good at scheming. However, they're cunning and deceiving to make up for it, manipulating several heroes. They also have some combat skills but get overshadowed by the heroes, and always tend to escape at the very last second before getting fully defeated, while yelling that they'll be back. However, it is seen that in the future they actually succeed in ruling the world, with the heroes working extra hard to stop him.
 * Bowser (Super Mario Bros) - They are evil, yet goofy. They also tend to gloat about themselves a lot, and appear to be somewhat overconfident. However, they are extremely powerful foes that the protagonist always uses lots of effort in defeating. However, their schemes have some plotholes. They can shift size whenever they want, but prefer to stay in a huge, giant form.
 * HIM (The Powerpuff Girls) - They're both Satan, and are masters of shapeshifting and disguise. They tend to be comical, yet deadly threatening foes to the hero, nearly the biggest threats in their own series, even succeeding in enslaving the world in the future (although HIM only ruled the world in an alternate future). Also, exists a rumor that Professor Utonium is a descendant of Jack and HIM is another one of Aku's transformations.
 * King Piccolo - They both have succeeded in ruling the world. They're also both Large Hams, and tend to share the same face expressions.
 * originally planned to finish Jack's and Aku's story with a theatrical feature-length film based on the series. However, the idea was abandoned after several delays and changed for a fifth season.
 * Aku is the first main villain of a Cartoon Network show that is not defeated at the original end of it. The second is Slade from .
 * In recent years, Aku has been subject to a meme based on a scene (particularly in Episode XLVIII), where he is apparently ordering a large pizza, but actually a bounty hunter, in which he says the line before hanging up. The meme typically revolves around Aku calling things "extra thick", which is purposely misspelled in the title of the videos as E X T R A T H I C C.