Goku is the main character of  Dragonball.  He is a pure-hearted, innocent, naive, good-natured boy, with a tail and a near-bottomless stomach.  He was found in the woods as a baby by a martial arts master named Son Gohan.  Son Gohan trained Goku as a small boy.  Unfortunately Goku also has a tendancy to transform into a huge ape (oozaru) when he sees a full moon.  In this state he has no control and goes on a rampage.  He also cannot remember anything that he did, when he was very young he transformed and squashed his grandfather.  Other than waiting until the night is over there are two ways to turn him back to normal, one is to cut off his tail and the other is to destroy the moon.  At the start of DB he is 12 years old.   But we don't find this out until the first Tenkaichi Budokai since he didn't know how to count until Master Roshi taught him.  Goku's naiveté gets him into a lot of trouble. He can't tell men and women apart by looking at them, this means to him, that he has to check.  This gets him in a whole bunch of trouble.   There are also quite a few words he doesn't know either.  At the age of 12, he agrees for Chichi to be his bride, but he thinks bride is a type of food.    Throughout his travels he meets many strange people, and changes some of their lives.  Its safe to say that most of his friends tried to kill him at one time or another, but were won over by his pure-hearted actions.  At the end of DB he's 18.