The “Original dragon” is a canon background concept that originates in Generation V and is related to the trio of dragons Reshiram, Zekrom and Kyurem. Alas, the franchise has done next to nothing with it, with the concept remained in the shadows ever since the mentions in Generation V.

The concept of an “original dragon” has a number of varied realizations in Fanon, such as ky-min's "Vahirom", mdsk-rb's "Kasedraru", and to a lesser extent F.U.S.E. Corp's "Perfect Kyurem", not to mention countless others, each going with its own design decisions and features.

See also: Drao

While the canon does not do much if anything with it, the “original dragon” is also largely adapted into its own thing in the Suocéverse in the form of the "Original Dragon" Drao. Barring further meta developments, though, this interpretation of the original dragon remains a still abstract lore element, though design decisions are pending for its inclusion in “Suocéverse Legends” N/A? .

At the time of latest update, the largest difference between the Suocéverse “original dragon” and the “original dragon” seen in some of the fanons above is that the Suocéverse one at the moment involves only the dragons Reshiram and Zekrom.

The dragon itself is an implementation of the concept of the Original Dragon, though the mechanics and metaphysics of it are not yet decided. In particular, the current temporary planning goes for two potential avenues of development:

• the Drao split into Reshiram and Zekrom, with Kyurem being a third, separate entity; moreover, Reshiram and Zekrom can fuse on their own accord if they have the means so (which likely include the Draco Plate) and none can impose the fusion upon the other(s), whereas the Kyurem fusions are a separate, parasitic sort of fusion.
• the Drao split into at least three dragons, themselves being Reshiram, Zekrom, Kyurem and a potential fourth separate entity; Kyurem and the other potential entity can fuse with the other two dragons, which can be done by force, but those fusions are not complete and thus become corrupted, lacking various elements that grant it full control and stability; moreover, the various dragons comprising the Original Dragon could in theory fuse with each other in pairs into incomplete beings, but the complete fusion does require full synchronization between all components.