Ender Dragon is the first boss in the game. It spawns only in The End. After it dies, it drops a dragon egg and a portal to the Overworld. It is resistant to water, lava. It destroys any block that it comes into contact with (apart from the Obsidian, Bedrock and End Stone), and its contact with any block causes a blast comparable to that of the TNT. That is why, putting up any sort of a bunker or a vault is completely pointless - it is mobility that counts while fighting a dragon. The Ender Dragon attacks your character only, it does not attack any other mob. It is protected by the Ender Crystals, which regenerate its health.
What also makes fighting the monster worthwhile, is the fact that you can obtain a lot of experience points (if you were to fight the dragon at the 0th experience level, it would make it rise to 78). Another positive aspect is the opportunity to unlock "The End?" achievement, for getting to The End alone, and "The End." achievement for defeating the Ender Dragon.
After the dragon dies, another one does not spawn after you enter The End. After you destroy it, and enter the portal, you will watch the only cutscene in the game. After that, you are transferred to your spawn point in the Overworld. There is no way to establish a spawn point, with the bed, in The End. Ender Dragon can also be encountered in the multiplayer mode and fight it with your team (unless the other worlds have been blocked by the administrator).
The most powerful boss in the game. Does not spawn, he can only be crafted with 4 Soul Stones arranged into the letter "T", and put 3 Wither Skull on top. It is more demanding than the Ender Dragon. After it dies, it drops the Nether Star, which is required to craft the Beacon.
The creature flies around and attacks by hurling explosive skulls, which can also cause the Wither Effect similar to poisoning. It is hostile towards all mobs and can wreak immense havoc this way. If placed underground, it will be digging his way to the surface itself. It is not possible, however, to create two Withers, which would fight with each other - after a while, they return to the neutral status with each other. The beast is also capable of regenerating own health. It is resistant to all factors, such as water fire, suffocation or damage from cacti. TNT explosives deal damage to the wither, but these are of low damage factor.
It is required to craft and destroy, to obtain the "The Beginning?" achievement, for spawning the Wither in the game world, and defeating it to obtain the "The Beginning." achievement. There is no limit on the number of created Withers, nor is there any limit on the number of Withers existing simultaneously.