There is a certain formula for the typical shonen anime protagonist. Any protagonist worth their salt tends to be a younger person with a big heart but a relatively middling sense of intelligence. They tend to be something of a genius — in the Japanese sense rather than the Western sense — in one very specific thing with a very specific sort of talent. A sprinkling of hotheadedness and a certain amount of a bottomless stomach tends to round out these characters, and it's all the better if their parentage is vague at best in the beginning, and something in their pre-birth past has a major effect on their future. Many of these tropes, as so many in shonen do, started in Dragon Ball.
Forty years after the beginning of the series, everyone knows who Son Goku is. He is the granddaddy of the modern shonen protagonist; Naruto, Luffy, and so many others run because he walked before them. The sheer scope of Dragon Ball can make it feel as though Goku hasn't really changed as a character overall. He is still mischievous and kind of dumb, something that Dragon Ball Super aped on to the point of it feeling like a character regression. Contrary to popular belief, however, Goku did have a lot of character development. It's just that most of it happened in Dragon Ball.
Goku Was Actually Different At The Beginning Of Dragon Ball
The story of the original Dragon Ball takes Goku from age twelve to age nineteen is, obviously, one of the most tumultuous times in any person's life. For Goku, it was probably beyond any imagining. Most American audiences were introduced to Goku a lot deeper into his story, as the airing of Dragon Ball Z on Toonami was the way that the franchise finally was able to succeed in the West. At that point in the story, Goku is married with a son and a full-grown adult. He's mastered a school of martial arts, won a world tournament, and saved the world quite a few times. This version of Goku, despite being still relatively young at around twenty-one years old, can only exist after the development he went through in Dragon Ball.
When the world first met Goku, he was a twelve-year-old boy living in the woods after the death of his grandpa years prior. He's clearly a little goofy, but incredibly strong and independent as a young man. He ends up being dragged out into the real world by Bulma on their quest for the titular Dragon Balls. In the beginning, Goku is actually incredibly sheltered. He doesn't know much about the world but is excited about it. This version of Goku is very much a little kid, a bit immature for his age, and excited about an adventure. He's even more excited about eating and fighting a little bit as well. This is pretty much who Goku started as and, while much of this continues, Goku does change a lot.
Goku starts changing a lot once the King Piccolo Saga ramps up. Goku's sense of morality was actually pretty skewed as a younger person. He was far more willing to go along with actions that would be easily side-eyed, especially during the Red Ribbon Army Saga, where it is very clear that very few people survived Goku's attack. While they were the bad guys, Goku never really gave a second thought to whether his attack would kill people. After Krillin's death, something fundamental in Goku changes. Goku isn't just out for a fight for the sake of a fight or to do something right, he is out for vengeance.
This is a major shift for Goku at this point. Until these major losses, he was a relatively carefree kid without much of a mean streak. He was training and growing, becoming stronger and looking for more ways to prove himself. Incidentally, Goku did good things while seeking fights. But his fight with Tamborine has a bit more sadism to it. He goes out there looking to hurt and kill Tamborine for vengeance. This exemplifies something darker in Goku in his youth. His fight with King Piccolo is a major moment for him too, and regaining his friends allows him to grow once again.
Piccolo Was A Major Mover In Goku's Development
Piccolo Junior, as he was once known, was also on a path of vengeance and domination when he met the now-older Goku. This Goku is the culmination of the strife in his youth, closer to the Goku of Dragon Ball Z but not quite there yet. This fight with Piccolo Junior is the thing that ultimately leads Goku to become the version of himself that lives in the hearts and minds of people across the world. It helps that this is one of the best fights in the entire franchise. This is one of the most knock-down, drag-out fights in shonen that leaves both characters exhausted and in tatters until the end — but this is where the audience sees the shift in Goku.
The old Goku would probably have gone for the kill or planned something else. But this Goku, older and wiser, asked for Piccolo Junior to be spared. He wanted Piccolo Junior to get stronger and fight him again, a move that he went on to repeat a few times. He doesn't want to lose a rival, and that makes him better. This is the character development coming full circle for Goku, and it all relates back to Piccolo himself, both as King Piccolo and the Piccolo audiences know and love today. Piccolo is, arguably, the most important villain in Goku's entire life. These are the major moments that shift Goku from being a kid who stumbles into situations to one who can be heroic in those situations while preserving one of his ultimate flaws.
Goku's story set the tone for shonen anime for the next four decades. So many characters have been built in his image as a result of his growth and change, but he was always a little different. Goku is, ultimately, a little bit selfish, and he never grows out of that. He loves a good fight, loves a challenge, and loves to get better and better. These things are the most important in the world to him. But Piccolo is where he starts to use his tendencies for real good, rather than doing so accidentally. Piccolo's sagas are what turn him into a hero rather than just a protagonist.
Goku is one of the most important characters in anime history. His impact on the world is impossible to quantify, and his legacy has spread throughout the genre for ages. But sometimes it is easy to forget how he got there and how he has literally grown into himself to become the hope of the universe. Some media don't do him many favors either, making it seem as though he's been completely static and never grew up. Goku did grow up, just like so many people around him and in the real world did. Just like Goku, so many people practiced their Kamehameha Waves and tried to be their best selves. Goku's character development is some of the most organic because it truly came from growing up, just like it does with all of us.
