Gohan is the first son of Goku. He has tramendous power as a boy because of his temper. He started out as a pussy. He was very weak. But without him Goku and Piccolo would have died in the fight with Raditz. Goku is getting the crap beat out of him by Raditz and that triggers his temper and he breaks out of the Sayai-jin space pod and headbutts Raditz .That allwed Piccolo and Goku to get the uper hand on him. The Piccolo started to train him for the arrival of the sayai-jins. Then Gohan started to grow a power-full bond between him and Piccolo. He did a great part in the fight against Nappa and Vegeta. He was doing good against Vegeta when he was in Ouzura form( Big o monkey). The he traveled to namek to get the dragon balls to wish back the people killed by nappa and vegeta (including piccolo). He fought the ginu force and freeza while on namek. Then he started to train for the android saga. He first turned ssj while training in the room of spirit and time with goku. He defeated Cell because of his temper cell killed 16 and that triggered his temper and he turned ssj 2 and killed cell. After the fight with Cell he stoped training and went further into his studies, like his mother always wanted him too do.Then he had to fight the buus and he need to get strongerso he trainined to be mystic. He did good untill he was obsorbed. But he survived.
I will add more about Gohan when I get the chance.