History
About 1000 years ago there was a great saiyan warrior who tons of power.
He transformed into into SSJ but he could only turn it while in the Oozaru form
which only happend during full moons. He had some much power that he did
not know how to control it and destroyed a planet and himself with it.
What it takes to go SSJ
There are a few of the main things a saiyan warrior must require to turn SSJ.
1. They have to be pure of heart... evil or good either one.
2. He must be very angry... such as when Goku went SSJ for the first time when Krillen died.
What happens when they go SSJ and what do they look like?
When someone goes SSJ their hair turns yellow and sticks up, their eyes
turn green, their bodies get larger, a yellow glow surrounds them,
and their strength, speed, sight, hearing, endurance, and many other things.
As they increase their SSJ level they get more powerful and their physical
features change.
What levels they reached
SSJ1 - Goku (first), Vegeta, Trunks, Goten, Gohan, Vegetto, Gogeta, Brolly, and Gotenks
SSJ2 - Gohan(first), Goku, Vegeta
SSJ3 - Goku(first) and Gotenks
SSJ4 - Vegeta and Goku(first/i think)(only in DBGT)