Signer Dragon

The Five Dragons are a series of Dragon-Type Synchro Monsters, introduced in Yu-Gi-Oh! 5D's. These legendary dragons play a part in the legend of the Crimson Dragon, as well as being connected to the Signers themselves. That connection being that these legendary beasts who are actually servants to the Crimson Dragon, were the ones who sealed an evilness within the Nazca Lines.

That same evil, which is now known as the Earthbound Gods, has reappeared once again in the world as Duel Monsters cards used by the Dark Signers.

So far 4 of the Five Dragons have been released in the OCG and TCG: "Stardust Dragon", "Red Dragon Archfiend", "Black Rose Dragon" and "Ancient Fairy Dragon". The supposed mechanical version of the fifth dragon, Power Tool Dragon, was released in Raging Battle in the OCG.

In the anime, Professor Fudo gave the "Stardust Dragon", "Red Dragon Archfiend" and "Black Rose Dragon" Duel Monsters cards to Rex Goodwin. As these three, along with the "Ancient Fairy Dragon" card were originally designed so that their corresponding Signer could activate the safety switches for the Old Enerdy system.

Members
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:

"Power Tool Dragon", which belongs to Leo, looks like a mechanized version of the fifth Dragon. Leo believes he is the fifth Signer, after asking Luna if Power Tool Dragon took part in the ancient battle between the Five Dragons and the Earthbound Gods, that she saw in her dream. Luna replies that maybe it did, just to make him happy, although she didn't think it was the same dragon, since such a robotic Dragon could not have taken part in the ancient battle, since it's too high tech.

Assault Modes
"Stardust Dragon" and "Red Dragon Archfiend" have their own "/Assault Modes": "Red Dragon Archfiend/Assault Mode" and "Stardust Dragon/Assault Mode". Both of them were Summoned by Yusei and Jack in a special episode.

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

Yusei Fudo
''Tsudoishi negai ga, arata ni kagayaku hoshi to naru! Hikari sasu michi to nare! Shinkuro Shoukan! Hishouseyo, Sutādasuto Doragon!!! "Clustering hopes become a new shining star! Become the path its light shines upon! Synchro Summon! Take flight! Stardust Dragon!"

Jack Atlas
''Ouja no kodou, ima koko ni retsu wo nasu! Tenchi meidou no chikara wo miru ga ii! Shinkuro shoukan, waga tamashii, Reddo Daemonsu Doragon!''

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

Aki Izayoi (Akiza Izinski)
''Tsumetai no honoo ga sekai no subete wo tsutsumikomu! Shikkoku no hana wo hirake! Shinkuro shoukan, araware yo, Burakku Rouzu Doragon!''

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

Booster Patterns
So far all the boosters for the 5D's (with the exeption of Raging Battle which has Power Tool Dragon and Stardust Overdrive which has Savior Star Dragon) has had one of the Five Dragons as the Cover Card:

Duelist Genesis - Stardust Dragon

Crossroads of Chaos - Black Rose Dragon

Crimson Crisis - Red Archfiend Dragon/Assault Mode

Raging Battle - Power Tool Dragon

Ancient Prophecy - Ancient Fairy Dragon

Stardust Overdrive - Savior Star Dragon