Pigman

A Pigman is a Pig in a humanoid form. Although currently not implemented into the game, their skin can be found within the game files, and their counterpart, Zombie Pigmen, have been part of The Nether since the Minecraft Alpha 1.2.0 Halloween Update. They have the same dimensions as the player. No coding is present within the game to spawn them.

History
Minecraft user Miclee came up the idea for Pigmen. He was given the Bacon Cape as a reward, but when Notch was asked for personal capes by other users, the Bacon Cape was taken away from Miclee to prevent further commotion.

Notch mentioned April 25th, 2011 that he might add Pigmen as NPC Villages' townspeople. In Beta 1.9 Pre-releases, a different Villager mob was introduced.

Regular pig models were changed in Beta 1.8 to have a protruding snout. Whether this will be applied to Pigmen or Zombie Pigmen in the future is unknown, although possibly unlikely due to them sharing the same shape as Zombie Pigmen, Giants, Zombies, Humans, and Players.

Trivia

 * The model used in the source is called a "Biped". A lot of other models uses this as a base, such as the Creeper model.
 * If you can find the skin file in your minecraft.jar, you can wear the Pigman skin like any other skin.