The Z Fighters in Dragon Ball are famous for their overwhelming strength. They are among the most impressive warriors in the universe, capable of protecting Earth against countless threats. The Z Fighters also have strategic minds, proving they have the brains to go with their considerable brawn.
Even so, not everyone is on the same level intellectually. Some characters stand out because of their gifted minds and knowledge of multiple disciplines, while others got the short end of the stick in the smarts department. Everyone knows Goku is far from being the cleverest character in the franchise, but who is?
Mr. Satan
Although he comes off as annoying and overly cowardly at first, Mr. Satan slowly reveals his true nature. He's not the proud warrior he pretends to be, just a slightly dimwitted but ultimately kind-hearted man. His relationship with Majin Buu develops his character, proving he is a worthy ally to the Z Fighters.
Still, for all his strengths, Mr. Satan isn't exactly clever. In fact, quite the opposite. He displays a shocking lack of common sense, often agreeing to face enemies that outrank him. He does have considerable luck, and that's a fortune, because he would've died if he didn't.
Yamcha
Yamcha was never the brightest character in the show, and his reputation only decreased as the story moved forward. He isn't unintelligent, per se--none of the show's characters are--but he is unfortunate. However, he was more knowledgeable at the beginning of the show. The show's early arcs painted him as a martial arts expert and talented bandit, a dignified character in his own right.
Eventually, Yamcha became a victim of circumstance until his character became one of the many storylines Dragon Ball dropped. It's a shame because he had potential; alas, he remained forever stuck in the same place, with the show hinting that his strength and intelligence had reached their limit.
Goku
At first sight, it might be easy to confuse Goku's naivete with stupidity. His child-like mind often plays for laughs in the anime, and many characters enjoy pointing out how dumb the things he says or does are. Goku is the ultimate animated himbo in many ways, but Dragon Ball never allows him to become a joke. On the contrary, his purity and innocence are one of his greatest assets, the things that make him so worthy.
Goku is also not unintelligent. He may be overly naive at times, but his mind never betrays him in battle or during any other potentially deadly situation. Goku is always alert and never underestimates his enemies, proving he is far sharper than anyone believes him to be.
Krillin
Level-headed and realistic, Krillin is perfectly aware of his limitations. He knows his place and his duty and always performs it to the best of his abilities. Krillin may be the calmest and strategic of the original Z Fighters, always looking for ways to survive against the increasingly challenging enemies they fought. And as a human, he needed to come up with clever ways to stay alive.
Krillin's mature approach to battle, and life in general, kept him from becoming a punching bag like Yamcha, or a forgotten legacy character like Tien. He also has something sorely missing from the other Z Fighters, and that's emotional intelligence. Krillin often doesn't receive the credit he deserves, but he deserves major props for always using his intellect in the best way possible.
Vegeta
Vegeta started as a villain before having one of the best redemptive arcs in the Dragon Ball saga. A fearsome warrior, he has a more savage approach in battle. However, he is never reckless or careless. Vegeta has an overly tactical approach due to his immense pride. He has a very analytical mind, planning his assaults carefully during his time as a warlord.
Vegeta is an intensely proud individual, and that's his greatest flaw. Indeed, his selfishness often clouds his judgment, preventing him from making wise decisions. In short, Vegeta lacks emotional intelligence, although he does show a remarkable talent for assessing others.
Master Roshi
It takes plenty of intelligence and outright knowledge to teach the mightiest warrior in the universe. Indeed, Master Roshi is leagues above all other characters in terms of wisdom. He teaches Goku the fundamentals of education--reading, writing, basic history--and the secrets and techniques of martial arts.
However, Roshi's instruction goes beyond simple training; it's a way of life, a philosophy that aids them in understanding the universe and their place in it. The show enjoys exaggerating Master Roshi's more earthly pleasures, but the wise teacher remains an imposing and, at times, inspiring figure.
Trunks
Future Trunks has more knowledge than any of the other Z Fighters, except for Piccolo. He is well-versed in all crucial events in history and the circumstances that provoked them. Moreover, he received a complete education from Gohan, putting him at an immediate advantage.
Present Trunks also proves himself quite clever. GT has several problems, but Trunks' character isn't one of them. On the contrary, he receives considerable development for the better, turning into a mature and capable young man on his way to become an even better man. Trunks runs Capsule Corporation successfully, and he doesn't even need to put his whole mind into it. Now, that's intelligence.
Piccolo
In all his iterations, Piccolo is devastatingly intelligent. He remains one step ahead of the Z Warriors during the King Piccolo arc of the original anime, proving himself a tactician without equal. Once he becomes an ally, he uses his abilities to protect the Earth, always offering insightful comments and evaluations about the situation.
Piccolo is also one of the show's best teachers. He trains Gohan, Goten, and Trunks, helping them understand the extent of their abilities before aiding them increasing them. Piccolo is also an excellent judge of character, making him invaluable for the Z Fighters. With unparalleled emotional intelligence and a unique perspective on the universe, Piccolo is one of the cleverest characters in the franchise.
Gohan
An academic at heart, Gohan is an intellectual who also happens to be an overwhelmingly powerful warrior. From childhood, he exhibits an inherent passion for learning. It didn't matter if he was studying books or martial arts techniques; Gohan had a thirst for knowledge that helped turn him into one of Dragon Ball's fiercest fighters and a successful academic, all before he was even out of his teens.
Fans remain divided over the course the character took after the Majin Buu arc. However, the fact remains that Gohan was always a model student, and it does make sense that he would want to dedicate his entire life to do it. He is the perfect combination of street and book smarts, a warrior whose mightiest muscle is the brain.
Bulma
Bulma is, quite literally, a genius. She was still a teenager when she invented the Dragon Radar. In Trunks' dystopian future, she built the time machine that saved the entire world. Past Bulma also shows a considerable understanding of the machine's inner workings, proving her innate brilliance.
Furthermore, Bulma builts multiple gizmos throughout the show, becoming a vital member of the Z Fighters despite her lack of physical prowess. At one point, she even successfully mimics and eventually improves on alien tech design, building Saiyan suits like the ones Vegeta used in Namek. Her inventions come in handy time and again. Her intellect allows her to escape the abandonment hell that so many other original characters fall into as the show progresses.