Wither

The Wither is an undead monster, that can be created if one puts arranges four soul sand blocks into a T shape (the same way one would an Iron Golem) and then add three Wither skeleton skulls on top of it. When killed they drop a nether star, which can be used to craft a beacon. It is said that its home is in the Nether, but they're mainly made in the Overworld.

Biology
The Wither is an undead mob resembling a limbless three skulled Wither skeleton. They are also black in color, and seem to be very strong as they take a long time to kill.

Society and Culture
While they don't appear to have an actual culture, they seem to be very nihilistic, as they attack and kill anything they see.

Notable individuals
Most individuals are destroyed after their creation.

Behind the Scenes

 * It is the second boss mob to be added to Minecraft. The first being the Ender Dragon.
 * According to Jeb, the Wither was inspired by Terraria, which has a summonable boss mechanic. The name itself is inspired by poison spell in another game made by Jeb called Whispers in Akarra.