Gunpowder

Gunpowder (previously known as Sulfur) is an item that can be obtained by killing a Creeper or Ghast and can be found in some dungeon chests.

Uses
Five units of gunpowder are needed to create a block of TNT.

History
In Indev, mob drops were randomized, so when a Pig was killed it could drop gunpowder instead of Pork (seen here). Gunpowder was renamed Sulphur in Beta 1.0, but reverted to its original term in version 1.3.

Trivia

 * Ghasts are not a recommended source of gunpowder because they float and spawn in the Nether, increasing the chance that the item will drop into a lava lake or inaccessible area.
 * Creepers are less likely to drop gunpowder if burned to death.

Schießpulver