Super Saiyan 1This stage was first reached by Goku in movie #6 as he fought Lord Slug. He didn't appear to be a Super Saiyan then, since his hair had a black tinge to it.
Officially, Gokou went SSJ1 for the first time in the Freeza Saga, after Furiza killed Krillin.
Physical description: Incredibilly increased muscle mass, and his hair turns Yellow.
Super Saiyan 2This level was achieved in movie #9, Gohan was told by Gokou to go SSJ2, he tried to go SSJ2, but reached a more incredible stage, The Ultimate SSJ Level, doing so he killed Boujack and the rest of his crew. This level is incredibly more powerful than SSJ1. SSJ1 was used quite frequently in movies #4-9, but SSJ2 had more immediate results. SSJ1 proved inefficient in stopping Boujack's crew, and when Gohan reached SSJ2, he easily overpowered the aliens.
Physical description: Alot greater muscle mass than SSJ1, and a few more inches of blond hair also pointing up. Occasionally accompanied by zapping silver lightning.Other saiyans have gone to this level also such as gokou,vegeta.
Super Saiyan 3Gokou first achieved this level during a fight with Majin Buu. SSJ3 was also used in Dragon Ball GT, but Gokou couldn't hold it due to his little body's lack of strength, although he does reach Super-Saiyan Level 4.
Physical Description: Gokou's physical appearance is more lean and menacing looking, with about 4 and half feet of flowing blond hair and a larger muscle mass. Also in this form the Saiyan-jin is Very Quick and Fast.
Note: Only Gokou and Gotenks have achieved this level. No other Saiyan's have achived it, but others have gone past this level such as vegeta.
Super Saiyan 4In this level they have increased muscle mass though. This is also the only stage with a tail. In SSJ4, Gokou is almost god-like, and he can use "Times 10 Kame-hame-ha." or "Ultimate Kame-hama-ha
Physical description: Although Gokou was wished by the Dragon Balls to become a child again, in SSJ4 form, he has his normal adult body with a bit more muscle mass. His upper torso is covered in redish/brown fur, his hair is black, and his eyes are red rimmed, pretty wicked actually.
OozaruWhen a Saiyan stares at a full moon, he will change into a 45-foot tall, monsterous monkey,Oozaru, in Japanese, translates to "Big Monkey . This is possibly the most powerful level under SSJ3. All Saiyan excluding Gokou and Gohan will be able to control themselves during this stage.It doesn't matter which full moon they look at in Dragonball GT, Gokou turned Oozaru by looking at the full Earth from Space. And, Vegeta had the ability to create a pocket-sized full moon when he first arrived on Earth to fight Gokou and Gohan that made him turn into the Oozaru.
Note: A Saiyan must have a tail to be able to turn Oozaru. If the tail is cut off, they revert to normal. If the tail is pulled out by the roots, the Saiyan will not turn Oozaru ever again.
Ougon (Golden) OozaruA level that was achieved by Gokou and Bebi-Vegeta in Dragon Ball GT. This is the most powerful form of Oozaru, actually, the most powerful of all stages that a Saiyan-jin can achieve, demonstrated by Gokou in DBGT.The main physical difference with the Ougon stage, is that the fur is yellow instead of brown.