Gohan is Gokou's and Chi Chi son he appears in the very first episodes and is one of the main characters in the program.
As a child his simian tail was removed Piccolo after Piccolo witnessed the power of Oozaru, Piccolo pulled it out on the basis that if he didn't there would not be an Earth to defend.
At a young age Gohan was left to fend for himself in the wilderness by Piccolo although a harsh training it worked and he realised some of his powers then.
Gohan is a strong warrior at one time he becomes the greatest warrior in the galaxy and gets the Z sword. But then Goku becomes the greatest warrior again and the Z sword brakes.
Gohan admires Piccolo a lot and often wears the same clothes as him. Gohan and Piccolo are good friends and Piccolo often saves Gohan's ass.
Gohan of course learns how to become a Super Saiyan but only reaches SS level 2. Like his father Gohan is kind and helpful, he looks quite like him as well.
He marries Videl Mr Satan's daughter who goes to his high school and has a child called Pan.
Before the Boo saga Gohan becomes a crime fighter known as the Great Saiya Man he fights crime and learns to be powerful without turning SS. He is successful and in the end Videl finds out and they fight crime together.
The reason he does not get more powerful is because he does not have the urge to fight like Goku and only fights when he has to. Akira Toriyami planned to make him more powerful and become the main character and call it Adventures Of The Great Saiya Man but people proffered Goku. I think that if it was not for that then Goku would have been the most powerful and got past SS 2.