Iron golems are 3 blocks high, and are automatically spawned in NPC villages and protect villagers from zombie attacks. Iron golems was released in the 1.2 minecraft update. Iron golems can be made out of 4 iron blocks and 1 pumpkin, see example here: http://minecraftupdate.net/wp-content/uploads/2012/03/2012-03-02_16.20.06.png. Iron golems damage 3 and a half, to 10 hearts damage. The golems also have some bugs too, here are some examples:

1) If an Iron Golem attacks a group of Zombie Pigmen, the whole group won't turn hostile towards the Golem. Only the one attacked will become hostile.
2) An Iron Golem riding a minecart will ignore everything, even if a target is in attack range.
3) An Iron Golem can spawn in a 2 block high area if the block above the two air blocks is glass.
4) Iron Golems can hit a target on the other side of a door. Their huge attack range also allows them to attack a target on the other side of a wall that is one block thick.
5) Iron Golems will attack wolves even when the wolves are tamed.

In villages where there is Iron Golems, there will spawn more of them, if there is more villagers, and the numbers will keep on going up because there is no limit, for numbers of Golems per village. A fun feature about Iron Golems is that, when it enters water it will turn passive.

That's the end of this tutorial blog post, if you got anythings that you think i missed, then please write it down in the comments. :D