Aku is the central antagonist of the cartoon Samurai Jack. He is also known as the "Master of Masters", "The Deliverer of Darkness", and the "Shogun of Sorrow". He was voiced by the late Mako Iwamatsu, who also voiced Master Offay from Super Robot Monkey Team Hyperforce Go! and General Iroh from the first and second seasons of Avatar: The Last Airbender.
Aku constantly antagonizes Jack, often attacking him when he is weak, and other times defending himself from Jack's own gambits. The two seem doomed never to defeat each other, for though Jack has defeated him on numerous occasions, Aku merely transforms into a creature and escapes, usually calling out a taunt over his shoulder, a fact that he is entirely aware of and even makes a reference to in "Episode XLVIII: Jack versus Aku".
While he's usually presented as a serious and threatening foe, Aku is also a source of comedy in the show, due to his outrageous design and sometimes wise-guy behavior, supported by Mako's over the top voice-acting.
The episode The Birth of Evil reveals Aku's origins. Long ago in the vastness of space, a great, formless evil arose. Before it could do harm to the universe, it was set upon by the three prime deities of the Aesir, Egyptian, and Hindu mythologies: Odin the All Father, Ra the Sun God, and Vishnu, the Supreme God and Soul. During the battle, the deities' assault was fierce, and despite the entity's attempts to resist, it was almost entirely destroyed, save for a single piece flung from the whole. This fragment drifted through space for untold time, until it eventually crashed to Earth during the Cretaceous period of the Mesozoic era. It is implied that this crash is the event that caused the extinction of the none-avian dinosaurs, although the crash occurred in modern day Japan as opposed to the Chicxulub impactor, which touched ground in modern day Mexico. The fragment developed over eons into an ominous forest of black spikes that devoured any who dared enter. Eventually the forest grew so large that the Emperor (Jack's father) decided to kill the evil at its source. Armed with a magic oil given to him by Buddhist monks, the Emperor and his cavalry rode into the heart of the forest, the Emperor himself the only survivor as his cavalrymen vanished one by one. Once at the black lake in the forest's center, the Samurai Lord doused an arrow into the oil he was given, firing it into the black lake. Unexpectedly, the oil's magic did not destroy the evil, but had the unforeseen effect of galvanising the evil into a human-like form, giving it sentience and shape-shifting abilities, and thus giving birth to the demon wizard, Aku.
Aku easily defeated the Emperor, trapping him to the side of the tree from which Aku spawned in order to watch as Aku destroyed the Emperor's home. The Deities, sensing the good in the Samurai Lord, summoned him to a secret place. Taking the good inside him, they forged used avatar bodies to create an enchanted sword that is capable of harming Aku. Armed with the sword and a magical suit of armor, the Emperor plunged into battle against Aku. In the end, the Emperor was victorious, but he was unable to destroy the demon, and so instead sealed him into the devestated wasteland. As he was sealed away, Aku vowed he would one day return. Shortly after, the Emperor's wife gave birth to a son. Determined to learn from the catastrophe, and aware that Aku may indeed one day return, the Emperor and his family determined on creating a plan, and thus orchestrated the events that would set Jack on his eventual years of training.
During a solar eclipse, the tree form that Aku was imprisoned in dissolved and Aku was released. In a castle, Jack was a young child and his father was telling him how he defeated Aku. After the story was done, Jack was left alone, playing with a toy sword. Suddenly, the castle was covered in Aku's shadow. Aku unleashed a vicious attack on the city. Jack's father attempted to get the sword, but Aku captured him before he could reach it. The Lord told his wife it was time to enact the plan they had prepared. Following the plan, Jack's mother escaped with him and the sword. Jack then started on his journey to prepare both physically and mentally for his confrontation against Aku.
Many years have gone since Jack left for his journey. His people, including his father, have become enslaved to dig up the resources of their land so Aku can begin to take over the world. After Jack completed his training, he came back and defeated all of Aku's demonic minions and freed the people of his land.
Jack then went to his tower to battle with Aku. After a vicious battle, Jack eventually overpowered Aku. However, before Jack could finish what his father started, a desperate Aku tore open a portal in time and flung him into the distant future, certain that he will be able to amass enough power to destroy him by then.
Unknown centuries passed before Jack reappeared into the world. During that time, Aku managed to terrorize and subdue the majority of the entire world, plundering its resources and making himself the undisputed ruler of Earth. Although he began with demonic servants to carry out his will, he later became enamoured with mechanical servants, and enslaved scientists to make the X-Model. All but one were eventually destroyed before the next generation of Aku's army were developed: the Beetle Drones. Successors to the X-Models, the beetle drones became the model for a series of insect-themed minions that served Aku well into the height of his power, and were his standard henchmen.
Hungry for more power, Aku established the Earth as a space-faring world, opening his ports to surrounding worlds in order to seize their riches as well. The influx of aliens, ranging from enslaved species to rough immigrants, have made the Earth a hodge-podge of a dystopian society primarily run by tyrants and gangs. The few bastions of peace and hope typically remain out of Aku's wide field of vision.
Since Jack arrived in the future, Aku habitually watches his progress through the world, with both of them taking every opportunity to destroy each other in an unending struggle.
Ikra was one of Aku's aliases, just one of several forms which Aku assumed in order to travel closely with Jack. Using his shifting abilities Aku changed himself to the appearance of a young woman with green skin, black hair and a black dress. She/He travelled with Jack across the desert, battling many dangers together. Under the guise of Ikra, Aku and Jack had formed a close bond (at one point Ikra even saves him from drowning in quicksand). Ikra told Jack that her father, like Jack's, had fought with Aku and having lost been forced to spend eternity trapped in a ring of fire and that she was on a quest to find a magical jewel in the desert which was powerful enough to free her father. When Aku reveals himself as having been Ikra the whole time he mocks Jack for having believed the story about her father.
The Hermit was another one of Aku's aliases, just one of several forms which Aku assumed in order to travel closely with Jack. Using his shapeshifting abilities Aku changed himself to the appearance of an old cranky hermit with green skin, white hair and a black robe. He travelled with Jack to find the Gems of Cronus, looking for one gem to the other, in order to resurrect Cronus. Unlike with Ikra, Jack saw through the deception and was ultimately able to turn the tables on Aku. In the ensuing battle Jack defeated and heavily injured Aku, forcing him to retreat.
Shapeshifting: Calling himself the "Shape Shifting Master of Darkness" at the opening of each episode, Aku can change into virtually any form he desires, from a giant dragon to a small insect, or even a beautiful woman. He can also change his size, liquefy 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, adapting to the situation. He is however limited to his own colour scheme, no matter what form he takes, it will always be black, red and green. Also, his true reflection will always appear, even in another form.
- Superhuman Strength: Aku can manifest considerable physical force when needed, though due to his shape shifting and mystical nature, he rarely utilizes simple brute force.
- Immortality: A significant aspect in the series is that Aku is ageless and immortal. Therefore, he needs no food, air, or water and his wounds will merely regenerate from any conventional injury. He can only be harmed and finally defeated by Jack's samurai sword.
Dark Magic: Aku, being a demonic manifestation of a formless evil, is naturally tapped into various dark forces. This gives him magical power beyond any mere mortal. There appears to be little to no limit to it, as he can perform acts of necromancy along with manifesting demons, energy projection and various supernatural feats. The powers he has demonstrated so far are:
- 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. He can also teleport beings through this ability.
- Pyrokinesis: Aku can breath streams of fire from his mouth and project it from his hands.
- Scrying: Using mystical forces, he can create mid air images to spy upon Jack and other enemies. He seems to need to be aware of their existence before he can track them.
- 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.
- Teleportation: Aku uses this quite often to appear before those he has business with, such as the Imakandi.
- Telekinesis: Aku has shown the ability to manipulate objects with his mind alone.
- Object Materialization: The ability to create objects out of thin air. He once used this ability to conjure gold, jewels, and treasure for the Imakandi.
- Interstellar travel: Aku is capable of interstellar travel at the speed of light.
- Necromancy: Aku has been shown in one episode to be capable of animating countless dead bodies, and bending them to his will, for they lack mind and soul.
- Weather Manipulation: Aku is capable of conjuring thunderstorms at will.
Known forms he has taken
- Bat: (he uses this form mostly to escape) used lots of times
- Scorpion: used in I and XXX also shown in opening titles
- Gorilla: used in I
- Billy Goat: used in I
- Squid: used in VIII and briefly seen in XXXVIII
- Manta Ray: used in IX
- Spiked Tubeworm : used in IX
- Spider: used in XXXVIII
- Kraken: used in I but also shown in beginning opening titles
- Cobra: used in XII
- Dragon: used in XIII
- Chinese Dragon: used in XXX
- Praying Mantis: used in XXX
- Mouse: used in XXX
- Frog: used in XXXIV
- Fish: used in XXXIV
- Flying Dragon: used in XXXVIII
- Army: used in XXXVIII
- Dark Mass of Shadow tentacles: used in XXX
- Human: used in XLVIII
Despite his nearly omnipotent abilities, Aku has a few weaknesses. These include:
- Color Scheme: Aku's shapeshifting is limited to his color scheme and will remain red, black, and green no matter what form he takes.
- Reflection: Aku's own reflection will reveal his normal form.
- Magic: Though Aku cannot be harmed by normal weapons and attacks, he can only be harmed, defeated and vanquished by Jack's sword and other mystical forces, such as divine weapons and power. Furthermore, the Goddess of Water and her 3 elemental servants are able to harm and defeat Aku with very little effort, although not at the same degree as three 3 gods Odin, Ra and Vishnu. Since Aku was a fragment of the greatest manifestation of evil, he can be destroyed by the strength and purity of a human's (and likely any other living creature) spirit, as stated by Vishnu. This can be seen by Jack's katana, forged from the purity and strength of his father's spirit, are able to inflict an extremely agonizing injury to him, judging by his scream. When possess by Aku, Jack, in his psyche, vanquish and exorcise the demon from him completely by the light of his spirit.
- Illness: In one episode (XLIII), Aku appears to suffer from flu-like symptoms, exposing his lack of immunity to catching diseases.
Aku is evil incarnate; he embodies the very essence of an evil overlord. Cruel and domineering to all he meets, it's obey or be obliterated with Aku. Arrogant and sadistic by default, 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". 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 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 has no remorse whatsoever about telling someone he will save their village if they obey his command, only to destroy said village as soon as he gets what he wants.
Despite this, he possesses a dry sense of humor and often jokes when in a good mood, frequently mocking Jack whenever he can and whatever he can. For instance, in one episode Aku holds a time portal just out of Jack's reach as Jack jumps for it.
He also provides humor to some episodes in more indirect, physical ways. For example:
- In one episode, Aku steals Jack's sword and ultimately strikes at him while Jack is utterly defenseless and immobile. At this point, Aku is as excited about his victory. Rather than piercing Jack's chest, the sword simply bounces off his skin with a metallic cling, leaving both opponents speechless. As soon as Aku sees this, his face is shown in close-up. He does not move, his pupils shrink and his flaming eye-brows extinguish with a sound like that of a loud bunzen burner being turned off abruptly.
- In the same episode, before Jack arrives at the location where they would fight, Aku was spying on Jack to loudly loathe his existence and await new oppurtunities for an attack. When Jack arrives at a junction in the road, he decides to leave his choice to fate. He picks up a stick and tries to "sense" the best destination by pointing it both ways. Following that, he throws the stick into the air and follows the path it points at after landing. During this entire scene, which lasts quite long, Aku is repeatedly shown as he spies on Jack. Each time, Aku has a plain expression and clearly has no clue whatsoever as to Jack's intentions with the stick. He doesn't move or even blink, he just sits perfectly still and continues to look dumbfounded until he finally realizes what Jack is about to do and sabotages the stick's landing direction.
- In another episode, Jack finds an ancient, inhabited, secret temple. Upon meeting the temple's grand master, Jack remembers Aku's ability to spy on him wherever he goes and loudly tells his host that he must leave immediately. The grand master then tells Jack he's blocking Aku's vision using what he describes as a large shield. The next scene shows large vehicles equipped with searchlights scouring the jungle (resembling search helicopters), followed by Aku glaring at and banging on his spying screen, which is showing white noise like a TV and clearly sounds like glass when he hits it.