Enderman Lore, as told by TheKingofSkulls.

Long ago, before the Overworld exsisted, before the Nether, before the pixels that make up Steve's body, there was the shining World of the End. The End was once rules by 12 Enderlords, who in turn were ruled by the Ender Dragon. Legend says that if the Ender Dragon were to ever die, one of the Enderlords would be selected to become the Enderdragon.

This started the Enderwar. The 12 lords divided themselves into two groups,The Nexus and the Overlords. These two clans battled for centuries over who would become the Ender Dragon, until one day, both clans were banished to alternate worlds, of nothing but bedrock, by the Ender Dragon.Soon, the World fell into it's current state, a wasteland of Endstone, towered over by the remains of the Enderlords' castles.

As for the banished Endermen, they started to create a new world for themselves, the Nether and the Overworld. How they obtained the building materials, no one knows. After the two worlds were made, the ones in the Nether soon died off, giving room to the resident cells and genes to evolve into the Nether mobs.

The ones in the Overworld, however, Lived on, and slowly de-evolved so they could only pick up certain blocks. The Overworld Endermen now oversee the Overworld, appalled at what has become of their creation. Horrible monsters, bizzare animals, and one human to rule over THIER world, took root in their land. Whenever they are forced to lay eyes on the new human, they sucumb to a fit of rage, and try to destroy the one who destroys their land.

Enderman are also made from a bizzare combination of Obsidian and Flesh, forming a semi-tough skin that is resistant to most things(thus making it one of the highest health mobs in the game). Due to the Obsidian, which is made by cooled lava, they are terribly hurt by water.Their teleportation is made by their Enderpearls,which is the heart of the Enderman. The remaining End Enderman have begun to re-build their glorious world, and rely on the Overworld Enderman to give them the blocks they need, hints why they steal blocks.

Also, Steve happens to be very ugly in Enderculture.