Son Gohan, was a master of martial arts. He has found Son Goku in the woods and he toke him, named him Son Gohan and raise him as his grandson.
But Son Gohan could not control Son Gohan, because the orders that was given to Son Goku was to destroy.
Son Goku was becoming more stronger and  more uncontrollable. One day Son Goku has suffered a mortal hit in the head and only because the good care of Son Gohan he managed to survive.
After that, Son Goku became a good natured kid, a little shy and a never-gives-up person, thanks to the hit and his adoptive grand father.
Son Gohan gave Son Goku one dragon ball, the one with the for stars and he said him that if anything happens he will be watching him, and because he is very strong he mast go to Master Roshi to train him.
Son Gohan was right; the bad has happened. Son Goku ,even after the hit to the head, transforms into Big Giant Monkey really strong and uncontrollable. In one of these transformations he killed him.
Son Gohan meets Son Goku another two times. In one martial art match (Son Goku has go to a witch to learn were is the seventh dragon ball, and for that he must win five other fighters. The last one was Son Gohan, that fight him without knowing who it is.)
Son Gohan because he were a good person, were and is now, an assistant of a woman that controls the fire forge. Son Goku went there to blow out a fire in the palace of Chi Chi's father.
I believe that without Son Gohan, Son Goku not only he would have not save the earth, but he would have destroy it!

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