Goku is the main character in Dragonball Z. He is a saiyan (a fighting race who at one time were almost the ultimate warriors).
All saiyan's have simian tails which means they can turn into powerful giant apes when they see a full moon. Goku's tail was cut off when he was a child.
As an infant he was sent to Earth to prepare it for an invasion but he bumped his head which made him forget his mission and turning him into the kind and helpful person he is today.
Goku's passion for fighting and his will to be the best is what makes him so good. He likes fighting strong opponents because it makes him stronger, when he is nearly defeated he always finds a way to defeat his opponents.
He marries Ox Kings daughter Chi Chi around the age of 16-17 not knowing what marriage is until he is told. When he is told he says "Sure why not". They have two children the first Gohan and then Goten.
Gokou only cares about fighting strong opponents and the rights off humans and other races, he does not care about Earth politics or Earth leaders.
When fighting Frieza he is the first to be able to turn into a Super Saiyan.
Gokou's saiyan name is Kakarot which is a play word on carrot, the word Vegeta the name of the planet he comes from and the name of one of his enemies who becomes his ally is a play word on Vegetable.