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." Enderdragons will also not be feasibly killed without a bow and arrow. They will boast armoured bodies, to which weapons bounce off of. To kill them, you will have to hit them square in the head or in the soft underbelly. They will drop massive amounts of experience. The Enderdragon can destroy every block (even bedrock) except End 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. Notch has stated that Enderdragon Eggs may be a possibility, and he has been working on them since the feature freeze. Enderdragons will also have unique death animations.

As of 1.9 pre-release 5, Enderdragons can be killed only by attacking their head repeatedly with a melee weapon or arrows. Defeating the Enderdragon will reward the player with many experience orbs and a single block of obsidian. It's likely that the obsidian block is only a placeholder for a later reward item. Because Enderdragons still don't seem to spawn in The End they require to be spawned through a modified mob spawner.

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 had not been enabled ingame yet. A community-made mod allows players to spawn Enderdragons by parrying with a golden sword.

On October 27th 2011, 1.9 Pre-release 5 was released and Enderdragons could finally be hurt. They still do not seem to appear naturally in The End and need mods or a mob-spawner to be brought into the game. However, when slain, it has a very distinct death animation: it will rise upwards, emit purple beams of light from its body while the body itself disappears pixel by pixel, until it's all gone, and the lights fade away.

Trivia

 * The name "Enderdragon" was first made known through a tweet by Notch reading "raqreqentba," which could be decoded using the ROT13 cypher, 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.
 * End 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 the area around (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.
 * As of 1.9 pre-release 5, Enderdragons:
 * Can only be hurt by the player attacking their heads or torsos, as the rest of their bodies are invulnerable.
 * Have their own death animation in which they levitate up to the sky while purple rays of light dissolve them.
 * No longer catch fire from lava or the fire aspect enchantment.
 * Reward the player with 20,000 experience points when killed by dropping a massive amount of experience orbs.
 * Drop a single block of obsidian when killed. This may be a placeholder, as Notch has revealed he has been working on Dragon Eggs.
 * Can only be hurt below the 127 block map height limit. Getting Enderdragons to fly above the limit (in creative mode, Overworld) will prevent any damage that could be done to them.
 * Can have their textures 'glitched' when viewed from far away. Their models also appears to shake when viewed at the edge of the render distance.
 * Have their own achievement called "The End" which requires defeating an Enderdragon. However, this has been tested and the achievement does not seem to work even if the player defeats the Enderdragon.
 * Enderdragon spawners will only be able to spawn a single Enderdragon, because the spawned Enderdragon will destroy it's own spawner upon appearing.