Dragonball Z

Gohan is the son of Goku, who is a Saiyan, and Chi-Chi, a human. Gohan was the first half-breed character in the series. Gohan has inherited his father's Saiyan powers and is able to become a Super Saiyan.

Saiyan Saga

Gohan has always had a certain "potential" within him that allowed him to nearly defeat Raditz as a child. After Raditz was defeated, Piccolo took him for training so he could prepare for Vegeta and Nappa's arrival. Gohan ran from Piccolo multiple times, but was found.(Note:This doesn't happen in the manga) Once, Gohan transformed into the Oozaru during the training, the giant ape that Saiyans change into during a full moon.Piccolo was shock to know about what can the Saiyans do during full moon,so he decided to destroy Earth's moon.After Gohan has finish 6 months of training with Piccolo,he fought against Nappa while Goku was rushing back to Earth from the North Kaio's place.Piccolo, grown attached to Gohan, died protecting him from a blast.

Gohan, Krillin and Goku all fought against Vegeta. Gohan transformed into the Oozaru state again, crushing Vegeta. His tail was cut off during the battle, ending the transformation.

Frieza Saga

Gohan played a small role in the Frieza Saga, going with Krillin and Bulma to find the Namekian set of dragon balls before Vegeta can make his wish for immortality.

Cell Saga

Gohan was present when Trunks brought warning of the androids. He went off to train with Goku and Piccolo for three years. He and Goku spent time in the Hyperbolic Time Chamber, enhancing their strength dramatically and allowing them to stay in their Super Saiyan form without it zapping any power from them.

After Goku fought Cell during the Cell Games, he chose Gohan to fight next. The fight was one-sided until Cell crushed Android 16's head, the kindest of the three, which untapped Gohan's potential, making him the first Saiyan, full-blood or no, to go to Super Saiyan 2. The transformation made Gohan superior, but brought out the primal side, and Gohan wanted to make Cell suffer for his crimes instead of stopping him. This lead to Cell blowing himself up and Goku, sacrificing himself, took Cell away from Earth.

Gohan,reaching Super Saiyan 2

Gohan, though happy he saved the world, was upset that his father died because of him. While mourning, Cell reappeared,and killed the Future Trunks,saying that he was more powerful than ever before. Gohan, angered that his father died in vain and that he let this monster live, powered up and was ready to fight.Suddenly,Vegeta rushed out from nowhere to attack Cell.After Cell had managed to defeat Vegeta,he tried to kill him with a ki blast,but the Ki blast hit Gohan's arm when he was trying to save Vegeta.For the final blast, Cell charged up a Kamehameha blast, ready to take out the entire Solar system. Upset and beaten, Gohan didn't try to stop him. But, after a heart-to-heart with his deceased father, he charged up a blast and, with Goku and Vegeta's help, managed to destroy Cell.

Majin Buu Saga

At age 16, Gohan switched from being home schooled to attending Orange Star High School. After going to Hercule City for the first time, he noticed a large amount of crime and powered up to Super Saiyan, becoming the 'Gold Fighter'. After questioned about wearing the same clothes as the fighter, he went to Bulma and made a superhero costume. Gohan then fought crime as 'The Great Saiyaman'. He then met Videl, Hercule's daughter, who quickly found out it was him. She agreed to let him keep it a secret if he entered the tournament with her.

Gohan ready to fight Buu

After a time, he heard that his father that he would be coming back for the tournament. After telling his mother how much the prize money was, he and his 7-year-old brother Goten were allowed to enter. He entered as the Great Saiyaman, but his match was cut short by Babidi's servants stealing his energy. He and the Supreme Kai went after Babidi and a strange creature called Buu. He was quickly defeated by Buu and believed dead by his family and friends.

In actuality, he was taken to the Kai's world. He was told that me may be able to pull out the magical Z Sword from a large rock. After much effort, he managed to pull it out. He began to train with it and ended up breaking it. Gohan let free the Elder Kai who helped him unlock his hidden potential. Afterwards, he was unable to go Super Saiyan anymore. He went back to fight Super Buu but was absorbed by him.

Dragonball GT

In GT, he had a minimal role. We find out that he ended up marrying Videl and they had a daughter Pan. He fought many of the major enemies, but did not defeat any of them.

Alternate Timeline

In Trunks' timeline, Gohan was Trunks' father figure and mentor. Gohan, outraged by Goku's death, became a Super Saiyan. He spent all of his time defending the world and training Trunks to become a Super Saiyan after all of his family and friends, with the exception of Bulma and Trunks, were killed. After defending Trunks from Androids 17 and 18, he ended up having to lose his arm. After hearing about another attack, he knocked out Trunks and went to fight alone. He was killed, and Trunks finally transformed after finding his mentor's body.