Son Gohan is Goku's oldest son. He is not important in Dragonball Z
until the Cell Series. Unlike Goku, Gohan does not really enjoy
fighting. 

Gohan was the first person to become Super Saiyan 2. He and
Goku killed Cell using a double Kamehameha. Gohan also killed Bojack. 

Gohan studies a lot because Chi-Chi told him not to fight and to study. Goten is his brother. Gohan also trains Goten.

 Gohan marries Videl and has one daughter named Pan. He also disguises as the Great Saiyaman. Gohan teaches Videl to Fly. 

When he was young, when Raditz trapped him in his
Saiyan Pod, He shows a lot of emotion because he saw his father getting beaten up. Gohan Cracked Raditz's armor.

He also went to the planet
Namek along with Krillin and Bulma to get the Namek Dragonballs to wish
Tien, Chaozu, Yamcha, and Piccolo back to this Dimension.

 Gohan was
taught by Kaioshin to use the Zet Sword.