King Piccolo Character Facts

King Piccolo came into being some 300 years 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 Namekian 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.
Being the concentrated evil that lived within the Nameless Namekian, King Piccolo's personality is the exact opposite of his good counterpart, Kami; as he is presented as a cold, ruthless, sadistic, and power-hungry villain with little to no sense of compassion whatsoever. He has demonstrated on many occasions that he is willing to do anything to accomplish his goals, regardless of how many innocent lives need to be taken in the process. Piccolo has also been shown to have a very warped and twisted sense of humor, often breaking out into a maniacal laughter after causing some form of death and destruction and creating a holiday where he would destroy a city every year on the anniversary of his take-over. 
Along with being extremely evil, Piccolo is also very arrogant, believing himself to be the most powerful being in the universe, and up until he was defeated by Goku, he was one hundred percent convinced that there was no one out there who could exceed his power. For all his many displays of arrogance, however, he was completely terrified of the Evil Containment Wave, presumably due to suffering its effects before, and completely freezes in horror the very moment it is performed. As a result, he made it his sole mission to eliminate all martial artists that either knew how or had the capacity to use it. 
King Piccolo, like most other villains, happens to be very intelligent, being able to think ahead and learn from his previous mistakes. This was shown when he destroyed Shenron after making his wish (so that no one would be able to use the Dragon Balls to stop his reign), as well as when his reincarnation decided to injure both of Goku's arms at the World Martial Arts Tournament (as opposed to before, when he ended up leaving one of them unharmed). King Piccolo also happens to be somewhat manipulative, as demonstrated when he used Emperor Pilaf and his associates, Mai and Shu, to gather the Dragon Balls for him. Rather typically, he decided to dispose of them when he figured that he no longer had a use for them. Despite being pure evil, King Piccolo shows mercy on a few occasions; The first time is when he leaves Master Mutaito to die but spares Mutaito's students Master Roshi and Master Shen; The second time is when he does not kill Yajirobe, who hid from him during his fight with Goku (King Piccolo can apparently sense power levels, as he states Master Roshi, Chiaotzu, and Tien are hiding from him, but he also seemed surprised when Chiaotzu appeared, thinking Roshi was alone). Later, after regaining his youth and becoming arguably more maniacal than before, he also spares the lives of Emperor Pilaf, Mai, and Shu, and later the life of King Furry (though he kills almost all of King Furry's guards). Also, during the worldwide announcement of his takeover, Piccolo stated that he deeply sympathizes with the criminals. According to himself, he sympathizes with them, because he viewed their imprisonment as being no different from his own, having been sealed within the electronic jar for many years.