Super Saiyan 5 is the fifth form of Super Saiyan a Saiyan can take, directly following Super Saiyan 4. This form is obtained by mastering Super Saiyan 4 and pushing it to its limit, similar to Super Saiyan 3. It can also be obtained when panicing about someone you care about about to die but you're too far away. When this happens, a wormhole appears and you teleport to them, creating a protective field and pulling them and everyone else around you back through the wormhole to where you came from. Like Super Saiyan 4, Super Saiyan 5 does not use alot of energy quickly, so it can be easily held. It's power is about as strong as the dark FIVE.
A Super Saiyan 5's hair grows to the length of a Super Saiyan 3's hair, except white. The fur on their chest also turns white as well. Other than this and a white aura, it looks like a white haired Super Saiyan 3 Super Saiyan 4. Their muscles are also really large, too.
The original user of the Super Saiyan 5. He is the first to use it, the first to master it, and generally the first to obtain new forms of each stage of Super Saiyan. It is safe to say that Goku is the master of the Super Saiyan.
Vegeta was the third Saiyan to achieve Super Saiyan 5. He gained it during the training on the Supreme Kai's planet with Bardock. He has still yet to catch up with him, despite mastering Super Saiyan.
Gohan was the fourth Saiyan to become a Super Saiyan 5. He gained it with the others on Supreme Kai's planet with Bardock.
Goten was the fifth Saiyan to become a Super Saiyan 5. He gained it with the others on Supreme Kai's planet with Bardock.
Since both Goku and Vegeta have mastered Super Saiyan 5, Gogeta has access to it as well.
Since both Gohan and Goten have mastered Super Saiyan 5, Gohanten has access to it as well.
Bardock was the second Saiyan to obtain Super Saiyan 5. He gained it while watching Goku almost die to the Negative Big Bang Kamehameha Maskeno. He gained it suddenly and created a wormhole doing so. This is the only time this has ever happened.