Ender Dragon

The Enderdragon is a new mob that is planned to be included sometime in the future, appearing in The Ender. Jeb has also made it clear that Notch plans to make dragons very difficult to fight without "enhancements." They will use the Dragon model Notch created, but instead are tinted black with purple eyes and have scales. Not much else is known about them, other than they are part of the "Ender" creatures.

History
Originally Dragons were a possible planned mob hinted at by Notch during the Spider Jockey update. He also mentioned that dragon lairs may be an addition. They remained a potential work-in-progress until the Enderdragon was announced.

Notch has in the past stated that if Dragons are added, they will not be able to be mounted because it would put pressure on servers in SMP. This has since changed to an Idea that MAY be added.

In September of 2011 Notch stated that "dragons will be added eventually".

On October 7th 2011 Notch revealed the existence of the Enderdragon.

On October 10th 2011 Notch released a video showing a small clip of The Ender which also shows an Enderdragon fly into the top of the frame. 

On October 11th 2011 Notch posted that Enderdragons are being released in Minecraft Beta 1.9.

On October 11th 2011 A player named stropping_Notch asked Jeb if Dragon riding is an idea, to which he replied it is. It is not clear whether this means it is an idea under consideration or not, however.

On October 11th 2011, Notch stated that "The dragon phases through terrain, and is 100% invulnerable now." This could be a joke, however, as he had just asked, 'How can I make it harder?'

Trivia

 * The name "Enderdragon" was first made known through a tweet by Notch reading "raqreqentba," which could be decoded using ROT13, translating to "enderdragon."
 * Before it was textured, Notch reported how he was afraid to texture it as it was a complicated model. In the end, the dragon model was so complex Notch reported that he gave up making the texture manually and invented a texture packer tool to aid him in adding the texture to the model. Notch also uploaded the code for the tool so others could use the pack.
 * The polycount on the dragon is higher than all models in Minecraft, Notch joked about how Minecraft was "going next gen" when deadmau5 mentioned this.
 * In terms of how difficult the Enderdragon will be to defeat, Notch tweeted that his design guideline for the dragon is "If I can beat it at all, it's too easy."