Super Saiyan Levels
Saiyan Forms
Saiya-jins are an extraordinary, barbarous and powerful race. (Note: In Japanese, "jin" means people; so that means that saiya-jin are "Saiya people") Their sole purpose in life was to fight and survive. At the beginning of the Dragonball series, we learn that they lived on Planet Plant. They shared this planet with a race called tsufuru-jin. The tsufuru-jins were an advanced race with many cities and highly-advanced technology. Their technology allowed them to fight against the naturally strong saiya-jins. The saiya-jins were strong savages who lived in wastelands attacking the tsufuru-jins at times. Because the saiya-jins had the natural ability of fighting using their bare hands, they were a force to be reckoned on. Fortunately for the tsufuru-jins, they were able to defend their planet with their technologies. Then, one night on the full moon, all the saiya-jins who had been exposed to the light of the full moon, underwent the change into Oozaru (Giant Ape) and easily crushed the tsufuru-jins out of existence. From then on the planet was called Planet Vegeta.
The saiya-jins used some of the tsufuru-jin technology to become the strongest race in the universe. The strongest being in the universe, Freeza, an evil creature, used the saiya-jins as mercenaries to take over planets for him and sell them. One day, the saiya-jins got tired of working for Freeza, so the king, King Vegeta, revolted with several of his loyal men. Unfortunately, he was killed along with his men. Freeza then destroyed Planet Vegeta in one giant blast, along with the entire saiya-jin race. Only a few saiya-jins survived, including Kakarotto (Goku), Prince Vegeta, Raditzu, Nappa, Taurus, Paragus and Brolli.
Saiyan
This is the typical appearance of a saiya-jin. A normal saiya-jin has black hair, a thick, strong, muscular body, and a unique tail. Saiya-jins have the excellent natural fighting ability that causes them to consume a great amount of calories daily. In order to provide these calories, they eat a lot. Goku, a low-class saiya-jin, consumes about 10 times the appetite a normal human would eat daily. Compared to humans, saiya-jins are extremely strong. Even when hit by a Bulma's car in the beginning of the Dragonball series, Goku was not hurt. He immediately stood up after he was hit.
Oozaru
This
is a form that is only for Saiyajins with their tail still attached, this
requires a moon in presents. Body size increases to about 55 feet; power
increases 10x. Appearance is that of an ape.
Super Saiyan
Freeza's worst fear... the Super Saiya-jin. This level is a legend early in Dragonball Z, but eventually becomes a natural form. Goku is the second person to ever reach this level, but is the first one we ever see doing it. When reaching this level the Saiya-jin's hair turns goldish blond, the eye's turn green, and his power level rises greatly. The Legendary SSJ mentioned throughout the series is Brolli. Super Saiya-jin are supposed to be ruthless killing machines, but we see that the Saiya-jin's personality barely changes after the transformation. The Super Saiya-jin level is triggered by emotional rage (usually). It can only be reached by someone with a pure heart of good or evil. Once reached the status of super saiya-jin, the Saiya-jin can go SSJ at will.
Ultra Super Saiyan
This stage is between SSJ and SSJ 2. During this stage the Saiya-jin's muscles greatly increase in size. The Saiya-jin becomes very strong, but also very slow. Attacks would do a lot of damage, but it is unlikely to hit the opponent. When Goku and his son, Gohan were training in the Room of Gravity and Time during the Cell saga, Goku demonstrated this stage to Gohan, and told him that it was useless because of it's drawback of making a saiya-jin usually slow. This stage's disadvantage is demonstrated as Trunks fights Cell and is beaten.
Super Saiyan 2
This stage was first reached by Gohan while fighting Evil Cell in the Cell Game. This stage is very much like the first Super Saiya-jin stage, but of course much stronger. Occasionally, the Saiya-jin who is in the form has electricity going around his body and through it. That's how you can tell the difference between SSJ and SSJ2. Also a Saiya-jin level 2 has slightly longer hair. This level is more superior than ssj level 1 in terms of strength and speed. It is also triggered by extreme rage.
Super Saiyan 3
Goku is the first and only person besides Gotenks to reach this stage. It is one of the strongest forms in all of Dragonball. You can tell a Saiya-jin is SSJ 3 when they have gold hair like all the other forms before it, and their hair gets really long and full. Also, the Saiya-jin's eyebrows disappear. This level is only achieved through training. After training in Heaven during the period of time after the Cell saga, Goku learned how to transform to ssj3. This form brings more power and speed, but because it uses more energy, a saiya-jin can only stay in this form for a short period of time.
Super Saiyan 4
This stage was made by TOEI Animation and was nothing to do with the original author of Dragonball, Akira Toriyama. During this stage the Saiya-jin's tail grows back. Their eyes turn yellow with a red outline around the eyes. The palm contains a hole that can absorb energy. Their back and most of their body is covered with red fur. The hair stays black, but gets long, not as long as SSJ 3. And again the Saiya-jin gets unbelievably powerful. Goku is the only real person to reach this level, but Buruma creates a device that turns Vegeta into a SSJ 4 also. This form is triggered by extreme rage, anger and sorrow.
Golden Oozaru
This stage is much like the regular Oozaru stage except that the fur is golden not brown and it's of course much stronger. This is also made by TOEI. To reach this stage a Saiya-jin must have a tail and must receive more waves from the moonlight. The only ones to ever reach this stage was Goku and Bebi Vegeta during Dragonball GT. Vegeta reached it while Bebi was inside of him and attacked his friends. He was eventually defeated by Goku.