Alias: Ma Junior ()
"My son.. In the future, you must avenge your father's death! Never let the roots of evil disappear!"
With these words, Piccolo Daimaou went out in a blaze, his knowledge and memory all transferred to his son, who took on his father's name, Piccolo.
Since the moment of his birth, he knew his mission in life. To conquer the world so that chaos and tyranny controls it, and to annihilate the man named Son Gokuu, who was but a boy when he killed Piccolo's father. As such, Piccolo had no childhood. From the moment he was born, he had no one to rely on, thus had to fend for himself in the wilderness, making himself stronger for the eventual day that he would be able to avenge his father's death.
It was not a happy time for him, perhaps the reason why he despised Gokuu so. Had it not been for Gokuu, he would have a father whom he could talk to, some companionship for those lonely times he spent in the wilderness. Piccolo's bitterness of the whole situation can be reflected in a statement he made as he threw Gohan into the wilderness to survive without any help: "If you must hate something, then hate your destiny ...which is just like mine."
Three years after his birth, he entered the Tenkaichi Budokai under the alias of "Ma Junior," his plan was to first rid himself of Son Gokuu, and then to take over the world, as his father did. Not one to under-estimate Gokuu (like his father did), he was very careful in carrying out his plans. Near the end of the tournament, he thought he had defeated Gokuu, but it turns out that he, too, under-estimated Gokuu just a little bit, and once again suffered defeat.
Having been defeated by Gokuu, he expected death, or at least total confinement; but to his surprise, Gokuu gave him a senzu, which restored all his energy. "How dare he take pity on me! I shall make him pay!" must've been the thought that raced through Piccolo's head.
Five years later, a new enemy arrived, forcing Piccolo to join forces with Gokuu. Even though the very idea of working with Gokuu made his stomach turn, the situation allowed no other alternative. By the time they finally defeated this new foe, Piccolo had found out the potential Gokuu's son had, and of his usefulness in the upcoming battle, against both the Saiyajins, and possibly Gokuu.
As the training with Gohan went on, Piccolo became more and more attached to the lad, even though he didn't want to admit it. However, when he saw that the boy was in danger, he could no longer stand still, and sacrificed himself to save the son of his mortal enemy. This was his true turning point. From this point on, he was no longer Gokuu's rival, but a true ally, even though he still had trouble admitting it to others.
In the upcoming fight with Freeza, Piccolo merged with the Namek warrior named Nail, and gained not only power, but knowledge of his true homeworld. Even though Nail promised not to let his own personality be in conflict with Piccolo's, in actuality, the two became more merged than Piccolo had realized.
Finally, in the fight against the cyborgs, he decided that his only chance of being able to defeat them was to merge with his father's counterpart. As Piccolo Daimaou was the evil side of Kami-sama, they were essentially the same person, but with completely different personalities. After seeing Cell, Kami-sama decided that it was finally time to allow for the re-merging of the two personalities, changing Piccolo and Kami-sama back to the person they were before the split occurred.
The re-merging finally made Piccolo whole, as he should've been. It also gave him the true power that he should have had (actually greater, since he also merged with Nail). As Kuririn said, "If Gokuu is to be considered a Super Saiyajin, then Piccolo must be a Super Namekseijin."
Even before re-merging, Piccolo was someone whom the other Z Warriors depended upon. Not only was Piccolo one of the best fighters, he had a great wealth of knowledge and wisdom. In the absense of Gokuu, most of the other Z Warriors looked to Piccolo. After re-merging with Kami-sama, both Piccolo's power and wisdom increased greatly. This was one of the reasons why Majin Buu chose to absorb Piccolo.
In the end, Piccolo developed into a very different person from what he started out as. Piccolo chose to stay at Kami-sama's temple, teaching Dende how to be a good Kami-sama, as well as to be out of his previous solitude.