Transform into Super Saiyan
Gohan, Goku and Chi-Chi's four-year-old son, was named after his adoptive grandfather. Physically, he resembles a young Goku right down to the tail and the likelihood to become an uncontrollable raging Giant Monkey when he looks at a full moon, while spiritually, he is good and pure of heart as well.
Because of his protective mother, Gohan, starts out as a wimp, but when the Earth is threatened, he reveals his tremendous potential as a fighter and uncontrollably "powers up" in order to rescue his father from a desperate situation. Because of this, Gohan is forced into training in preparation for the eminent arrival of the evil Saiyans. As a result, he becomes quite a fighter in his own right with much of his training coming at the hands of Piccolo, the former arch enemy of Gohan's father, Goku.
The training begins as survival training. Gohan is abandoned for six months in the wilderness battling, among other things, hunger, scorpions, Sabre tigers, and dinosaurs. Then comes constant and intense fighting against Piccolo to train him in the art of war. His mission: "to kill the Saiyans and save the Earth". He is taught many things at the hand of Piccolo such as "you don't see the enemy, you feel him". The special bond causes Piccolo to step in front of Nappa's mightily blast to save Gohan's life. But, after all, Gohan was the only one that ever treated Piccolo as a friend.
Initially caught between "wimp" and "warrior", Gohan's loss of nerve in the battle against the Saiyans costs his friends dearly. Haunted by his failure, he is determined to make up for his cowardice and volunteers to travel to Planet Namek to search for the source of the original Dragon Balls, so that he can wish his friends back to life. And he comes through in the end of the final battle as he looks at the moon, turns into a Oozaru Saiyan and lunges toward Vegeta to fell the planet.
His power when initially kidnapped and placed in the spaceship was 710. This jumps to 1307 when he sees Goku hurt and to 2800 when he goes to fight after Piccolo's been hurt. His tremendous power is accounted for by the incredible mix between Earthling and Saiyan which produces an even stronger being than either human or Saiyan alone.
Gohan travels with the Z fighters to Namek to find the dragonballs, and uses his amazing power to pummel freiza to the ground.
A few years after He sends Garlic Jr. Back into the Dead Zone, with the help of Piccolo and Krillin.
During the Cell Saga, Goku and Gohan train inside the Time Chamber to get ready for the Cell Games. Once inside Gohan remembers the times where he let down his friends back on earth during the Saiyan Saga, and caused them to die. He uses these memories to transform into a Super Saiyan for the first time. From then on, Gohan is the most powerful fighter in the universe. During the fight with cell, Gohan transorms into Super Saiyan level 2 after seeing the death of Android 16, and easily destroys Cell, but at the cost of his father's life.
Seven years after the Cell Games, Gohan is now a teenager, going to high school, like a normal kid. But things heat up again after the Z fighters hear of the World Fighting Tournament, and decide to enter. Gohan, while fighting an opponent, is attacked from behind by some thugs who steal all of his energy. This energy is used to revive Buu, the evilest villan in the universe.