Pre- Dragon Ball
King Piccolo came into being some 300 years before the beginning of original Dragon Ball sometime after a Nameless Namek on Earth attempted to assume the position of Guardian of Earth, he was denied the position due to the evil that occulted within (a guardian's motives must be pure, but the Nameless Namek also wanted the job for the power it brought). As a result, the Namekian concentrated and trained to relinquish the evil within; which conspired into producing two separate entities — if one should perish, the other would also. This resulted in two beings — the concentrated evil being known as King Piccolo, and the pure being known as Kami. At first, the name "Piccolo" was a reference to the wind instrument, but then a revelation by Mr. Popo to Bulma meant it translated to "different world" in Namekian.
Piccolo created several offspring and watched as they terrorized and killed helpless citizens and destroyed the cities they lived in, but stepped in himself later on after his sons were killed by Mutaito's pupils, including a young Master Roshi and a young Master Shen who were the only two who survived. Master Roshi and Master Shen could not as much as lay a finger on Piccolo, and Mutaito soon steps in, but is himself outclassed and left to die by Piccolo.
Mutaito manages to survive however, after being nursed back to health by his two remaining pupils, but before he could heal his wounds, Mutaito left, in shame because he lost in front of his two students. While Master Roshi never lost faith in his master, Master Shen did, and the two parted ways, with Master Roshi escaping to the mountains while Piccolo continued to kill human after human and destroy city after city.
Several years later Mutaito, carrying an electric rice cooker in a bag, reunites with Master Roshi in the cave Master Roshi was staying in and the two track Piccolo down for the final confrontation, which by this time most of Earth's population had been slaughtered. They find Piccolo in the ruins of a city, which is hauntingly quiet, and Mutaito wastes no time launching his attack on him, this special technique is revealed to be the suicidal Evil Containment Wave technique. Piccolo is trapped in the electric rice cooker and Mutaito dies, and sometime afterward Master Roshi personally tosses the rice cooker into the deepest depths of the ocean.
Afterwards things slowly return to normal, with the cities being rebuilt and the Earth being repopulated, and over time people eventually forget King Piccolo ever existed, with the exception of Master Roshi, Master Shen and of course Kami. Some, such as Tien and Yajirobe, heard the tale, but dismissed it as a mere bedtime story.
Dragon Ball and meeting a boy with a tail
Decades later he is released from his confinement by Emperor Pilaf, and King Piccolo decides to have all the current and former finalists of the World Martial Arts Tournament murdered, thereby removing all those who might be able to learn the Evil Containment Wave. To aid him in this, he spits out two eggs containing his first two sons Piano and Tambourine.
Tambourine quickly goes about the task, his first victim being Krillin, and he also dispatches Goku shortly after by blasting his Nimbus Cloud apart and throwing him down to the ground, though he survives. King Piccolo then spits out an egg containing a third son, Cymbal, who he assigns the task of gathering the Dragon Balls. King Piccolo seeks the Dragon Balls so that he can wish to regain his youth and full power.
When King Piccolo senses that Cymbal has been killed, he orders Tambourine to hunt down the assassin. Guided by Emperor Pilaf's Dragon Radar, Tambourine arrives at Cymbal's last known location to discover Yajirobe and Goku, and in a vengeful rage for Krillin's death, Goku kills Tambourine. Again sensing that another of his sons has died, King Piccolo decides to deal with the fighter responsible personally. Upon arriving, King Piccolo confronts Goku, and despite his age he easily defeats the boy (though King Piccolo was forced to admit that Goku was an exceptional fighter for forcing him down to the ground once). Goku is left severely beaten and near death. Master Roshi then challenges King Piccolo (using the last two Dragon Balls as a lure), attempting to trap him using the Evil Containment Wave. Master Roshi is able to catch the demon king in the wave, but when he attempts to hurl him into a container, he misses at the last second. The attempt leaves Master Roshi completely drained, and he dies shortly after swearing to King Piccolo that his plans will never come to fruition.
King Piccolo is then able to gather the Dragon Balls to summon Shenron. Chiaotzu attempts to make a wish himself to prevent King Piccolo from doing so, but is killed before he can finish, allowing King Piccolo to wish for eternal youth, becoming much more powerful than before since he was returned to his physical prime. However, before Shenron can disperse, King Piccolo kills him with a single blast to prevent anyone else from using the Dragon Balls against him.
With no one left who can properly challenge him, King Piccolo decides to savor his victory, rather than all out destroy civilization like he did the first time, and instead overthrows King Furry to become the ruler of the Earth. As part of entertaining himself, he institutes several evil policies such as releasing all criminals and a more planned system of destruction.
He is then confronted by Tien, who has now learned the Evil Containment Wave Technique but cannot perform it as the electric rice-cooker which would have been used to seal King Piccolo is broken (in the anime, Tien successfully performs the wave, but Drum is caught in it instead, and the rice cooker is destroyed before Tien could trap him). King Piccolo decides not to get his hands dirty, and instead spits out an egg containing Drum, his most powerful son yet. The battle between Tien and this new son, Drum, is of course in the Namekian's favor, and King Piccolo orders Drum to finish Tien off, but a much stronger Goku arrives just in time and quickly kills Drum with a kick so hard that it knocks his eyeballs out.
King Piccolo and Goku face off again with Goku blocking every attack King Piccolo tried, and Goku manages to punch King Piccolo into Piano with his crushing weight and Goku's strength, killing his son.
A fierce battle ensues, with Piccolo briefly gaining the upper-hand a couple times when he manages to knock off Goku's Power Pole (after which he is able to fire a weakened version of the Explosive Demon Wave), only for Goku to survive. After being unable to destroy him, King Piccolo resorts to a cowardly effort; he uses Tien as a human shield, threatening to crush his skull if Goku moves a muscle. Upon discovering that King Piccolo has killed Shenron and the Dragon Balls no longer exist, Goku resigns himself to do whatever King Piccolo wants despite Tien's pleas. King Piccolo then throws rocks at Goku with great force, costing the young hero the use of his legs and left arm. Satisfied, King Piccolo throws Tien aside and prepares to finish Goku off.
Realizing that he still had his right arm usable, Goku eventually blasts a Kamehameha from his right hand, propelling himself toward his enemy in the sky, punching a hole clean through King Piccolo's chest, mortally wounding him. Though shocked that he has been killed, King Piccolo decides that Goku has only won for now and his legacy will continue; when Goku isn't looking, he uses the last of his energy to spit an egg containing his final offspring/reincarnation. After imploring his son to avenge his death and destroy Goku, King Piccolo finally succumbs to his wounds and explodes.
Powers and Abilities
King Piccolo was at one time the strongest person on Earth. He was easily able to dominate most of the martial artists on Earth and was only stopped when Master Roshi's master sacraficed his life to seal King Piccolo inside an electric Rice Cooker. Being the original other half of Kami, King Piccolo has his power level and abilities though he uses them more viciously. After having his youth restored King Piccolo was stated to be at 260 for a power level.
Explosive Demon Wave - A very powerful blast that is fired from one hand while the second is gripped around the wrist to support the blast. This is one of King Piccolo's most powerful attacks.
Eye Lasers - King Piccolo is able to fire a quick and precise red energy laser from his eyes to nullify an enemy attack or to quickly kill a weaker enemy. King Piccolo used this to damage Goku's leg during their fight.
Great Namek - The Namekian ability to increase their size to giant proportions. King Piccolo was shown increaseing his size though not to the extent his son Piccolo or Lord Slug were able to.
Magic Materization - King Piccolo is able to conjure various objects from thin air. He is never seen doing this though is can be assumed this is how he creates his throne in multiple places and because both Kami(his good half) and Piccolo(his son) can perform the technique.
Masenko - The user places their palms above their head and fires a yellow energy beam comparable to the Kamehameha wave.
Mouth Energy Wave - King Piccolo is able to fire an energy blast from his mouth as a surprise attack. This attack was powerful enough to kill Shenron after he granted King Piccolo's wish for youth.
Mystic Attack - The Namekian ability to extend their arms for surprise attacks.
Pokopen - A corrupted version of the Namekian ability to reproduce asexually. King Piccolo creates various Namek like monsters like Tambourine, Drum, Cymbal, and Piano.
Telekinesis - King Piccolo is able to move objects with his mind.
Telepathy - King Piccolo is able to communicate via telepathy