The Birth of King Piccolo
Roughly 300 years before the events of Dragon Ball, the Nameless Namekian was given the opportunity to become the Guardian of Earth. However, the current Guardian at that time felt a horrible evil lurking deep within the Nameless Namek and would not allow him to claim the throne until all of that evil was expelled. The Nameless Namek meditated, and in Age 461, found a way to use a technique called fission, which would expel the evil from within him. However, the evil that was expelled manifested itself into the being later known as King Piccolo. The Nameless Namek, who now called himself Kami, could only watch as King Piccolo began a reign of terror over the Earth that would result in the deaths of thousands of people, due to them both sharing a single life line.
In an attempt to take control over the Earth, King Piccolo created several offspring, each of which were powerful mutated spawn. He ordered his mutated offspring army to attack and destroy Earth's cities and kill all of the people. The killings went on for some time until they eventually attacked the dojo of Master Mutaito. Though these skilled and powerful martial artists were able to fight and kill a few of King Piccolo's minions, this battle came with a hefty price.
Only two of Mutaito's students survived the battle, Master Roshi and Master Shen, and they narrowly managed to destroy the remaining minions. King Piccolo himself soon arrived on the battlefield and before Roshi and Shen could even attempt to attack King Piccolo, he used his finger blast to send them flying. Eventually, Master Mutaito stepped in and saved Roshi and Shen, only to also find himself heavily outclassed by King Piccolo's horrible power. Defeated and left to die, Mutaito is taken and nursed back to health by his two surviving pupils and goes on to continue his training alone in the mountains.
Several years later, Mutaito reunites with Roshi and the two head out to find Piccolo for the final confrontation. They find Piccolo in the ruins of a city, where Mutaito wastes no time revealing his new technique: the Evil Containment Wave. Using an Electric rice cooker specially designed to trap evil, Mutaito launches the wave and successfully traps King Piccolo in the jar. As a result of performing such a powerful attack, Mutaito dies, but not before telling Roshi to throw the jar into the deepest ravine he could find. Mutaito then dies and Roshi fulfils his final wish by throwing the jar into a very deep ravine.
The effects of the King Piccolo wars were cataclysmic on Earth. Thousands if not millions of people were killed and hundreds of cities and towns completely demolished. Some of the greatest martial artists and other warriors were also killed off, leaving only those such as Master Roshi and Master Shen left to defend the Earth, and subsequently take on pupils of their own. As centuries passed and Earth's population began to rebuild, the story of the King Piccolo wars became nothing but a fairy tale.
Rebirth of King Piccolo
Main article: King Piccolo Saga
Almost three centuries after the end of the King Piccolo wars, the evil Emperor Pilaf somehow managed to find the jar containing King Piccolo sometime during the 22nd World Martial Arts Tournament and was able to successfully release him in hopes that he could team up with Piccolo in order to conquer Earth. Upon his release, King Piccolo had naturally grown old and decrepit from spending so many years in the jar, and he soon after spawned Piano to serve as his attendant. Sometime later, Pilaf tells him about the Dragon Balls, which Piccolo decides to obtain in order to wish for his youth back. As a result, King Piccolo made his first order of business to eliminate all of Earth's most powerful warriors so that he would not be opposed. In order to do this, he spawned Tambourine, whom he sends out to the World Martial Arts Tournament arena on Papaya Island to steal Goku's four star Dragon Ball and list of all of the fighters. Tambourine arrives just after the tournament had ended, so he simply steals the list of fighters, but not before killing the young Krillin who attempts to stop him from taking Goku's Dragon Ball. Goku and the others soon arrive to find Krillin dead. Goku then decides to track down Krillin's murderer. Using the Dragon Radar Goku chases down Tambourine only to be easily defeated due to his exhaustion from the tournament earlier that day.
Goku later meets Yajirobe, who kills another of King Piccolo's spawn, Cymbal after he attacked them for Yajirobe's Dragon Ball. Goku eventually kills Tambourine and finally comes face to face with King Piccolo himself. After putting up a decent fight, Goku is eventually defeated by King Piccolo and appears to be dead. Master Roshi, Tien Shinhan and Chiaotzu eventually attempt to stop Piccolo as well. Roshi attempts the Evil Containment Wave but accidentally misses when transferring him into the jar. Master Roshi dies as a result of the move and all of the Dragon Balls are stolen. King Piccolo then summons Shenron and wishes for restored youth. Chiaotzu attempts to stop him from making his wish by calling out one of his own, only to be quickly killed by King Piccolo. After making his wish, Piccolo also destroys Shenron and then heads for the castle of King Furry. Together with Piano at his side, King Piccolo easily takes over the castle and declares himself the new King of Earth. Sympathizing with imprisoned criminals, King Piccolo frees all convicted criminals from prison. He also declares the anniversary of his takeover May 9th (May 13 in the Funimation Dub) to be Piccolo Day and reveals he plans to choose a sector each year where his celebration will be held ending with it's destruction.
Sometime later, Goku recovers at Korin's Tower and retrieves the Ultra Divine Water, which greatly boosts his power. He arrives to find Tien Shinhan alone and trying to stop Piccolo himself, but only to be getting mercilessly beaten by Drum, another of King Piccolo's spawn. Goku saves Tien and kills Drum, and finally sets his sites on King Piccolo as well. After a long and epic struggle, Goku finally kills King Piccolo, but King Piccolo plays his final card, which is spitting out an egg containing his reincarnate, Piccolo Jr. King Piccolo then dies and all is returned to normal. Goku eventually meets with Kami who agrees to resurrect Shenron. After Shenron is resurrected, a wish is made to revive all those killed by King Piccolo and his minions, including Master Roshi, Krillin and Chiaotzu. Goku then spends the next three years training with Kami and Mr. Popo, preparing himself for battle at the next World Martial Arts Tournament where he will face King Piccolo's reincarnate. King Piccolo's reincarnation, Piccolo Jr., mostly referred to as just Piccolo, ultimately turns good and joins Goku in protecting the Earth. Piccolo also maintains King Piccolo's connection to Kami which allows the Dragon Balls to continue to exist until Piccolo and Kami re-emerge and a new guardian has to be chosen. In the GT Timeline, Piccolo Jr. ultimately sacrifices himself to save the Earth from the threat posed by the Black Star Dragon Balls and travels to Hell to keep the villains in line after helping Goku escape.
Despite his takeover of the central government, King Piccolo is mostly forgotten by the general population of Earth by the time of the Cell Games with only those directly effected by his actions such as the Dragon Team and King Furry remembering his reign of terror.
In Dragon Ball Online, Piccolo remained alive as one of Earth's defenders and at some point had even become aware that some of the monsters that his father had spawned many years ago had survived the King Piccolo wars. Some were secretly incubated in places such as Pilaf's Castle, and others that had bred naturally in the wild. Piccolo became aware of their existence, but determined he could not resolve the situation on his own, and so he accepted it.
In Age 853, a while after the Namekians had resettled on Earth, at Grand Elder Moori's suggestion, Piccolo and a few other Namekians capture these monsters and keep them secured. In the midst of this, some Dragon clansmen started to research the monsters and were able to master handling them. This knowledge leads to the birth of Poko Priest class. Additionally, some of the Namekians who escaped to Earth ended up settling near King Piccolo's old throne in the Isuri's Lake area and became corrupted by evil as a result.
In Age 940, the Evil Egg born from the evil in the hearts of the Namekians who immigrated to Earth, is first discovered. It is placed under a strong seal for safekeeping. In Age 972, the black Namekian Naraku is born from the sealed Evil Egg. Naraku recruits other evil Namekians to form a group which eventually become known as the Dark Namekians. Like King Piccolo and his Demon Clan before them, Naraku and his Dark Namekian followers would seek to conquer Earth, resulting in them coming into conflict with the other non-evil Namekians lead by Grand Elder Moori. The Dark Namekians eventually allied themselves with New Namek's destroyer Mira and the Time Breakers. Piccolo himself opposes the Dark Namekians by monitoring their home base in Isuri's Lake and later sends in the Time Patrol who defeat Naraku and the rest of the Dark Namekians in Age 1000.