Ender Dragon

The Ender Dragon is the first official boss mob to appear in Minecraft (with the second being the Wither). It only naturally spawns in The End. This mob uses the dragon model Notch created, but utilizes a texture more reminiscent of an Enderman, being black and scaly with purple eyes.

Appearance
The Ender Dragon is a large, black dragon with glowing purple eyes. It is the largest and most detailed mob in the game, being made of 61 cuboids, more than any other model. It has a few dark gray features, such as the wings and various other parts of its body. Similar to Endermen and Spiders, the Ender Dragon's eyes are visible through darkness, so you can see it coming from anywhere in the End.

Behavior
The Ender Dragon will destroy any block it comes into contact with, except Obsidian, End Stone, and Bedrock. Instead of destroying them, the Ender Dragon passes through them creating explosion effect identical to that of a TNT explosion. When hit, an Ender Dragon makes roaring, growling and snarling noises.

The Ender Dragon has a purple boss bar that appears at the top of the player's screen. This bar indicates the remaining health of the resident Ender Dragon. Each End dimension houses a single Ender Dragon whose health is periodically charged by nearby Ender Crystals. Destroying an Ender Crystal while the Ender Dragon is being charged by it (indicated by a series of circles appearing between the Ender Crystal and the Ender Dragon) will cause the Ender Dragon to take additional damage instead of being healed.

Once killed, the Ender Dragon will appear to have beams of light spontaneously erupting from its body. It will then explode, dropping enough experience to bring a player from no experience to level 78 (12000 - 10 drops of 1000 experience, one drop of 2000 experience).

It will also spawn an exit portal with a Dragon Egg on top. Entering the portal will activate a text cutscene that lasts for an average of 8 minutes, 30 seconds. After the cutscene, the player will be teleported to his/her spawn point in The Overworld. The cutscene can be skipped by pressing the key, and will instantly send the player to his/her spawn point/Bed in The Overworld. The player may return to the End after defeating the Ender Dragon, however there will be no new dragon.

The Ender Dragon will only attack the player and does not attack other mobs besides the player.

On the Xbox 360 edition, the Ender Dragon's behavior is much different, making it easier to defeat. After flying around the obsidian towers for about 30 seconds, it will come back down and hover over the unfinished bedrock portal, and remain there for about 30 seconds. It is wise to build a staircase up to the top of the bedrock portal so that while it is hovering over the portal, you can continually strike it with a weapon, preferably a diamond sword.

Also on the Xbox version, the Ender Dragon fires projectiles at the player, but they don't deal too much damage.

Strategy
The most common and easiest strategy to defeat the Ender Dragon is to destroy all of the Ender Crystals before attempting to fight the Ender Dragon, as any damage done to the dragon can be quickly undone by the crystals.

When the Ender Dragon charges the player, it is directly facing the player. This gives the player a good chance of attacking its head to deal the most damage; attacks that hit any other part of its body cause only one-quarter (plus one point) of their normal damage. But if the player decides to attack it, he/she will have less time to try to avoid its attack. The impact of the Ender Dragon's body and wings cause damage to the player, as well as knockback. The highest armour and weapons, preferably all enchanted, are recommended. Because of the Ender Dragon's speed and flight, projectiles are favored over melee approaches. The Ender Dragon's immense health and evasive nature require a large ammunition stockpile. At least 2 full stacks of arrows are recommended since most will miss.

Lava is useless, as it is immune to fire damage. Water is also useless, as it will take no damage from water and will destroy the block, however it can be used to make a "safe zone" which Endermen will teleport out of. Knockback enchantments are useless unless the enchantment is on grade 8 or higher (this is possible in SMP with modifications). Snowballs have the potential to stun-lock an Ender Dragon as its recovery time is slower than the firing rate of snowballs. Due to a quirk of how it reduces damage taken, snowballs and other projectiles, such as Ender Pearls and Eggs, that normally cause no damage to entities will deal one point of damage to the Ender Dragon. Beds, which explode in the End, can be detonated when the Ender Dragon is nearby, causing considerable damage to it. Snow and iron golems are some what ineffective and rarely attack the dragon if at all.

Negative splash potions do not seem to affect the Ender Dragon. The potion hits and detonates as per normal, but the dragon does not flash red like when hurt and no apparent effect is seen on it. (Tested in SSP, and with Splash Potions of Poison, Instant Harming, Slowness and Weakness.)

To avoid fighting the endermen, do not look at them with your cross hair. Alternatively equip a pumpkin in the head gear slot which covers up your cross hair allowing you to look where ever you want. This strategy's down fall is that it obstructs your vision making it hard to keep an eye on the dragon. Invisibility will also prevent aggression by Endermen. Since you have to remove your armor in order for invisibility to be effective, and the Ender Dragon itself ignores invisibility, this is a dangerous strategy. 

Ender Dragon in the Overworld or Nether
Using a modification, or the export-import feature of an external editor like MCEdit, it is possible to place one or multiple Ender Dragons into an Overworld or Nether map.

In the Overworld the Ender Dragon employs much the same attack strategy, flying and wheeling and recoiling if hit by arrows or snowballs. Generally the Dragon remains above the player, making holes in any hills it may encounter and when charging the player it can plough a track across the terrain launching any mobs or entities it may encounter into the air in much the same manner as when striking the player. If the player retreats underground, the dragon continues to attack, mainly from above the horizontal plane the player is in, and in the process gouging large tunnels through the landscape and doing a lot of damage to the terrain.

In the Nether the effect is much the same, the Dragon carves tunnels through both netherrack and Nether fortresses, and over time can carve out quite a large volume. If the Dragon flies through water or lava, like most other blocks, they are replaced by air and do no apparent damage to the Dragon. In essence, the Dragon can pass through the landscape with impunity.

If multiple Dragons are present, only one health bar shows.

Xbox 360 Edition
In the TU9 Update, the Ender Dragon spits out "Ender Acid". The Ender Acid is purple, much like the particles around the Enderman. They also fire a type of Acid Ball similar to Ghasts, Blazes and Fire Charges, but with a more purple texture, which cannot be deflected. Like the PC version, they can also destroy/grief blocks placed by the player.

Also, instead of the portal being spawned underneath the Ender Dragon's death, it is spawned in the middle of the island as soon as you enter the End. However until the Ender Dragon is defeated, it will remain deactivated, and the Dragon Egg will not be on its podium. Until it has been killed, this is used by the Ender Dragon as a nest, where it will hover over it and attack the player with "ender acid".

One final difference between the Xbox and PC versions is that some of the Obsidian Pillars have iron bars surrounding the crystal. This prevents the player from shooting it from a distance with a bow, ensuring the player has to climb some of the Pillars.

Video
''Note: The video states the Ender Dragon is the only boss. It was made before the Wither was implemented.''

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 Ender Dragon was announced.

Notch has stated in the past that if dragons are added, they will not be mountable as it would put too much pressure on SMP servers.

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

On October 7th 2011, Notch revealed the existence of the Ender Dragon.

On October 10th 2011, Notch released a video showing a small clip of the End that also shows the Ender Dragon 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 Ender Dragon.

On October 12th 2011, in a Reddit post Notch also said, "They will be different dragons. The Ender Dragon 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, Notch stated in a twitter post that "Dragons have 6 limbs", consisting of 2 wings, and 4 legs.

On April 28th 2012, Jeb mentioned that he wouldn't be adding any more boss mobs until he makes the Ender Dragon "more fun first". Despite this, the Wither was added before any changes were made to the Ender Dragon.

Trivia

 * Contrary to popular belief, the Ender Dragon cannot be harmed by any mob other than a player or explosions. Therefore, the dragon will never purposely attack another mob, including a Wither.
 * Sword enchantments have no effect on the Ender Dragon. (Tested with a sharpness 32000 sword in SMP.)
 * The Xbox avatar item 'Ender Dragon Pet' has the description 'A cuter, friendlier version of his bigger, less playful Minecraft sister.'- implying that the Ender Dragon is female, which is strange since gender doesn't exist in Minecraft.
 * The Ender Dragon has its own separate mob folder containing separate designs: the old gray skin and the newer black skin.
 * The Ender Dragon flies at 10 times the player's normal walking speed.
 * An Ender Dragon's attack can cause Endermen to chase after it and attempt to attack it to no avail, should they survive the devastating attack. This also works with blazes, wolves, and zombie pigmen (only works in creative due to spawn eggs being available to creative only).
 * The Ender Dragon's hitbox is larger than the Ender Dragon itself, causing players to be pushed away from it.
 * You can get a plain white spawn egg that reads Spawn Ender Dragon by typing /give [player] 383 1 63, which is the item ID. However, when you try to spawn it, you cannot and it does not really work as anything.
 * Firing large amounts of arrows at the Ender Dragon when it is above the 256 block map height limit will create a "flux", or large amounts of glitched arrows in a spherical pattern, that, when the Ender Dragon descends below the 256 block map height limit, will continually damage it until each arrow has been used. If there are any arrows left in the flux after the Ender Dragon dies, they will shoot out in all directions. If the arrows were launched using a mod item that causes arrows to home in on a target, then the arrows will find a new target to home in on, meaning that if you are in the End, then every Enderman there will start to attack you.
 * As long as the Ender Dragon is alive, the space texture of End Portals, as well as the player's view in the End, will have a slight multicolored static overlay to it.
 * If you go beyond the "island" in the End, the Ender Dragon will constantly attack you instead of circling around before striking.
 * If the Ender Dragon is killed when there is no solid ground below, the portal to the Overworld will appear approximately where the Ender Dragon died.
 * If you spawn the Ender Dragon in a world and turn the difficulty to peaceful, the Dragon will stay and not disappear.
 * The Ender Dragon can't destroy Minecarts with Chests, making them a good alternative to store your items while in the End. Just store them in an interdimensional Ender Chest. Keep plenty of spares.
 * If you set a Superflat world to the End biome (9), and go to 0,0 either by teleporting or moving there, the Ender Dragon will be there, and killing it will drop a portal to the real End. There will be a separate Ender Dragon in the real End.
 * Ender Dragon makes the same crackling sound as a firework when it dies.
 * The Ender Dragon from the TU9 update is the only version of it that actually has a working projectile.
 * Ender Dragons can push other Ender Dragons around.

Notch-related trivia

 * The name "Ender Dragon" was first made known through a tweet by Notch reading "raqreqentba", which could be decoded using the ROT13 cypher, translating to "enderdragon".
 * On Reddit, Notch referred to the Ender Dragon as a she, and suggested her name to be "Jean?" in the same manner he called the Player "Steve?".
 * Notch joked about how Minecraft was "going next gen" when deadmau5 mentioned this.
 * Before it was textured, Notch reported that he was afraid to texture it as it was a complicated model. In the end, the dragon model was so complex Notch stated that he gave up making the texture manually and wrote 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.
 * In terms of how difficult the Ender Dragon is to defeat, Notch tweeted that his design guideline for the dragon is " [If] I can beat it at all, it's too easy."
 * Notch has uploaded a video showing why Ender Dragons will not spawn in the main world, as they would destroy any block they come into contact with.
 * On Reddit, Notch explained why Ender Dragons destroy matter.