Creeper

Creepers are hostile mobs that spawn in light levels of 7 or below. They pose a significant threat to new players, due to their dangerous ability to explode.

Offense
Creepers follow the player when they are within 16 blocks, and attack by exploding. They make a hissing sound before doing so.

Combat
It is best to use a Bow when fighting creepers, however a strong sword like an Iron or Diamond sword can also be used. Another possible method is to ignite the creeper with Flint and Steel and run away.

Charged Creepers
Charged Creepers are sub-types of regular creepers that will be added in Update 0.12.1. They only spawn when lightning strikes within a 5 block radius of a creeper. They have a larger explosion, and do much more damage to the player and terrain.

Trivia

 * Creepers are possibly the most recognized of all Minecraft mobs.
 * Creepers can be very hard to see in large grassy biomes, due to their green color acting as camouflage. This makes them a larger threat in these areas.
 * Creepers were created accidentally when, in the making of the PC edition, Notch tried to make a Pig.
 * When Creepers explode in water it can only hurt other mobs and players, but cannot destroy blocks.
 * Creepers do not make any noise when approaching the player, thus often taking player by surprise, but do make a hissing sound when about to explode.
 * Creepers have a different explosion look then PC and counsel. In this version the explosions are just steam effects.