Iron Ingot

Iron ingots are a metal ore used for crafting.

Natural generation
Iron ingots have a chance of appearing in stacks of 1 to 4 in dungeons, and in stacks of 1 to 5 in strongholds, abandoned mineshafts, villages, and nether fortress chests.

Iron golems
Iron golems drop 3-5 iron ingots upon death.

Zombies
Zombies have a 8.5% chance of dropping 1 iron ingot, 9.5% with Looting I, 10.5% with Looting II and 11.5% with Looting III.

In the Pocket Edition, zombies will not drop any iron ingots.

Trivia

 * Iron Ingots are the most versatile item in the game, being used in 27 crafting recipes. The second most versatile item is Wood Planks with 23 recipes. Technically, if the Nether Reactor Core is counted, Iron Ingots are used in 28 recipes, but the Nether Reactor Core is exclusive to the Pocket Edition, and some crafting recipes that use them are not in the Pocket Edition (such as Iron Doors).

Eisenbarren Lingote de hierro Fer (lingot) Vasrúd Iron Ingot 철괴 IJzerstaaf Sztabka żelaza pt-br:Barra de Ferro Железо (слиток) 铁锭