Ender Dragon

The Enderdragon is an upcoming mob that is planned to be in the 1.9 update. It exists only in its native dimension, The End.

This mob will use the Dragon model Notch created, but it will be black and scaly with purple eyes compared to a normal dragon. Like other dragons, the Enderdragon will have 6 limbs; consisting of 2 wings, 2 legs and 2 arms.

Jeb has made it clear that Notch plans to make the Enderdragon very difficult to fight without "enhancements." The Enderdragon can destroy every block(even bedrock) except White Stone and Obsidian, which they pass through harmlessly. Nothing else is known about it at this time, other than the fact that it is one of the few creatures that inhabit The End.

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.

In September 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 End which also shows the Enderdragon fly into the top of the frame. 

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, or whether it would apply to the red Dragons or the Enderdragon.

On October 12th 2011, in a Reddit post Notch also said, "They will be different dragons. The Enderdragon will probably become larger, and the ones in the main world will be this size, won't go through terrain, and will be red because dragons are red."

On October 12th 2011, in a twitter post Notch also said: "Dragons have 6 limbs" Which would consist of 2 wings, 2 legs and 2 arms.

On October 13th 2011, 1.9 Pre-release 4 was released along with The End. The Enderdragon exists in the code, mostly functional, however the dragon has not been enabled ingame yet. A community-made mod allows players to spawn Enderdragons by right-clicking while holding a gold sword.

Trivia

 * The name "Enderdragon" was first made known through a tweet by Notch reading "raqreqentba," which could be decoded using ROT13, translating to "enderdragon."
 * The Enderdragon may be the game's first boss mob.
 * According to Notch on Reddit, there will only be one Enderdragon in the End.
 * 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.
 * Made of 61 cuboids, 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."
 * On Reddit, Notch explained why Enderdragons destroy matter.
 * White Stone and Obsidian are the only blocks the Enderdragon cannot destroy, though it can pass through them.
 * It is likely that defeating the Enderdragon would be the only possible way to leave End without dying.
 * If a monster spawner is hacked to spawn enderdragons, most of their body parts (limbs, torso, head etc.) will be inside debug boxes, which appear like white squares. It will make no attempt to attack a player, but instead will fly to (0,0), which coincidentally is the location at which the player enters the End.
 * On October 12 2011, Notch uploaded a video showing why Enderdragons will not spawn in the main world, as they will destroy any block they come into contact with.
 * If you hit an Enderdragon with an arrow, they will deflect the arrow.
 * The Enderdragon has two separate mob folders containing two separate designs; the old gray skin and the newer black skin.
 * When an Enderdragon destroys a block by means of flying through it, an explosion effect identical to that of a TNT explosion occurs.
 * Currently, Enderdragons do not have firebreath. It is unknown if they will in 1.9, or if they will just ram everything with their head. (Ouch)