Signer Dragon

The Five Dragons are a series of cards, introduced in Yu-Gi-Oh! 5D's. These legendary dragons play a part in the legend of the Crimson Dragon, as being connected to the Signers themselves. That connection being that these legendary beasts who are actually servants to the Red Dragon God, were the ones who sealed an evilness within the Nazca Lines. That evil being the same one that's been battling the Signer's, that up until now being represented within Dark Signers.

Each of the five Signers possesses one of the Five Dragons. Currently, all five dragons have been shown, although only four have been named and associated with a Signer:

Although Power Tool Dragon appears with the other four Dragons during the second ending theme, it's unlikely that it is one of the five Dragons, as it belong to Luka, who is not a Signer, and a different Dragon appears with the other four Dragons alongside the Crimson Dragon. Also, Power Tool Dragon is a Machine-type, while the four named Dragons have all appeared to be Dragon-types.

Buster Monsters
Along with the Five Dragons there are a series of monsters known as "/Buster" monsters.

Although not exclusive to the Five Dragon series, "Stardust Dragon" and "Red Dragon Archfiend" have their own "/Buster" versions: "Red Dragon Archfiend/Buster" and "Stardust Dragon/Buster". Both of them were Summoned by Yusei and Jack in an anime tour special.

Summoning Quotes
In the Japanese anime, when Synchro Summoned one of the Five Dragons, their corresponding Signers chant a quote that describes them.

Yusei Fudo
"Clustering hopes become a new shining star! Become the path its light shines upon! Synchro Summon! Take flight! Stardust Dragon!"

Jack Atlas
"The ruler's heartbeats will now file through here! Take witness to its creation-shaking power! Synchro Summon! My very soul! Red Demons Dragon!"

Aki Izayoi
"Chilling flames engulf the entire world! Pitch-dark flower, set into bloom! Synchro Summon! Appear now! Black Rose Dragon!"