Goku is the hero of Dragon Ball Z Kai and the most powerful warrior on Earth. When the Saiyans arrive, Goku learns the mysterious secret of his own past: he is a Saiyan formerly named Kakarot. As a baby, Goku was sent to Earth to destroy the planet, but a head injury caused him to forget his mission. Instead of growing up to become a terrifying super villain, Goku was taught to fight on the side of all that is good by his adoptive grandfather Gohan.
Goku's one-time archenemy, Piccolo, is the second-strongest being on Earth. Born as a concentration of Kami's negative spirits, he can create powerful energy blasts, split into as many as four separate entities, and regenerate limbs that have been destroyed or severed. A native of the planet Namek, Piccolo originally dreams of ruling the world, but he reluctantly joins forces with Goku to defeat the Saiyan invaders. This uneasy alliance eventually grows into a strong bond between the two warriors. Piccolo also develops a special relationship with Gohan while training the young boy in Goku's absence. Gohan's willingness to befriend Piccolo gradually changes the Namekian's outlook on human life.
Krillin is Goku's longtime training partner and best friend. The two warriors met as students of the legendary martial artist, Master Roshi. A short, bald fighter, Krillin provides comic relief in tense situations as he tries to keep up with Goku and some of the other more powerful warriors. A skilled fighter in his own right, Krillin is forever loyal to Goku and saves his friends life on multiple occasions.
Named after his adoptive grandfather, Gohan is Goku's son, and he is every bit as pure, honest, and honorable as his father. After the arrival of the Saiyans - and Goku's subsequent death - Gohan becomes a vital player in the fight for Earth's survival. Piccolo, a former enemy of his father, takes it upon himself to develop Gohan's skills while Goku is absent. Initially a wimp, Gohan's training under Piccolo and his participation in battles of increasing brutality allow his skills to fully emerge.
Tien is a three-eyed warrior originally trained by Master Roshi's arch-rival. He defeated Goku at the World Martial Arts Tournament, and his powers are capable of striking fear into the bravest of fighters. His techniques include levitation, bombs of concentrated energy, directing blinding flashes of light at his opponents, and splitting his body into as many as four separate entities. Tien is an eager martial artist who readily accepts the challenge of testing his skills against the Saiyan invaders.
Chiaotzu has the power to stop people in their tracks and communicate via telepathy. This miniscule, white-skinned, red-checked being is the devoted companion of Tien Shinhan. Despite originally fighting against Goku, Chiaotzu time and again proves that he is a true hero at heart. The bravery he displays in the battle with the Saiyans is further evidence of his noble spirit.
An aged and legendary master of martial arts, Roshi has accumulated great power and knowledge in his lifetime. He's lived for countless years on a deserted island with only a turtle for companionship - hence the nickname "Turtle Hermit." His island serves as a rallying point for the Z-Fighters, and Roshi himself - although old, bald, and wrinkly - is a fearsome fighter in his own right. Master Roshi taught Goku and Krillin much of what they know about the martial arts, including how to harness the awesome power of the Kamehameha Wave.
Master Roshi's lone weakness is a disturbing fondness for pretty girls and sunny beaches.
Once a notorious bandit, Yamcha eventually became a longtime ally and close personal friend of Goku's. His best friend is a shape-shifting cat-like creature known as Puar, which may explain why he typically has trouble with the ladies. Although his physical gifts pale in comparison to Goku and Tien, Yamcha makes up for his deficiencies with a true hunger to improve as a warrior.