Crimson Dragon

The Crimson Dragon is the embodiment of the Red Star, a god. Long ago, before the Inca, the "People of the Stars", (also known as "Signers") called upon the "Red Star" for aid to save their lands from the Wicked Gods that threatened the peace of their civilization. The "Red Star" answered their call and came down from the heavens in the form of a Great Red Dragon.

The Crimson Dragon then sealed away the Earthbound Immortals, which we now call the Nazca Lines with the help of its servants, the Five Dragons. However consequently he lost Ancient Fairy Dragon to them, as the Earthbound Immortal Uru dragged her in with it when the Dark Gods were defeated.

Fortune Cup
The Crimson Dragon reappeared during Yusei and Jack's duel when "Stardust Dragon" and "Red Dragon Archfiend" battled.

Once again in their rematch, the Crimson Dragon appeared. However, everyone was witness to it and with the four Signers present on the Cup, its appearance was more defined than the last time. Each Birthmark was clearly represented and the dragon's head also changed. During the duel, the legendary Dragon God transported Yusei, Jack, Luna and Akiza into an alternate dimension and showed a disturbing vision in which Satellite is being destroyed by an unknown force and in its place, a dark mark resembling the Spider appears.

Dark Signers
The Red Dragon God shows itself once again to the four Signers at Rex Goodwin's place. As he invites them into, right after Yusei and Akiza's second duel concludes. As Goodwin reveals to them some secret concerning the Red Dragon. That being according to Goodwin that some sort of "fate" has been derived from the Crimson Dragon power's, one that to those who are Signers cannot escape from.

That same so called fate was the one responsible for that Yusei and Jack could arrive to New Domino City.

After the King of the Underworld finally revives and heads towards New Domino City, where the Condor Geoglypgh is, the Dragon God appears in the sky, and takes the Signers, along with their companions, to where the ultimate fight will be held. Though it also transports Yusei, Jack and Crow´s D-Wheel´s too.

After Yusei defeats Goodwin in the Ultimate Shadow Turbo Duel, The Crimson Dragon arrives, using Majestic Star Dragon to gain physical form, and destroys the King of The Underworld by flying right through it. It disappears soon after.

WRGP Arc
During season 2, the Dragon appears towards the conclusion of the duel between Leo and Luna against Lucciano. As Lucciano's Machine Emperor Skiel's attack towards Leo caused him to be blown off the riding lane, the Dragon uses a a sphere that emerges from its claw, which ultimately engulfs the falling Leo, just to land him safely on a bridge that was below them. After this, it disappears.

Yu-Gi-Oh! The Movie: Super Fusion! Bonds That Transcend Time
The Crimson Dragon is also going to play an important role in the battle against Paradox. So far it is not known what exactly it will do but it has been seen adding Yusei when he travels back in time and protecting Jaden from an attack by Sin Stardust Dragon.