The Creeper is a hostile mob that will ambush players and explode, causing damage to the player and the surrounding blocks. Unlike Zombies and Skeletons, Creepers will not catch fire in direct sunlight, meaning they can wander around unharmed any time of the day until it is killed. The creeper will still be aggressive during the day, unlike spiders. Creepers spawn in the overworld at night and in locations with a light level of 7 or less, just like regular hostile mobs (though they do not have a Spawner in vanilla minecraft.) They are especially dangerous as they are almost completely silent (except for footsteps and their hissing noises when ready to explode), and their explosion is devastating at short range. Creepers run from Cats and Ocelots[1] and will even ignore the player to run away when a feline is too close. The Creeper has gained considerable notoriety among Minecraft players for their infuriating habit of sneaking up on the player and killing/hurting them and/or damaging structures. The safest way to engage a creeper is from a distance by shooting two fully charged arrows at it with a bow so it cannot explode near the player. Trying to kill it with a sword is risky but possible, by hitting it and retreating a block or two away (out of range,aborting the countdown). This can be repeated until it dies, but mind your footing behind you! If the creeper is climbing to reach the player, say emerging from a hole, knocking it back down is also likely to abort the countdown.
Swimming or wading creepers can be easily dealt with using melee attacks, since in water the knockback is far enough to put the creeper out of range. (Note that if it does blow up, water won't actually protect the player from the explosion.) Alternatively, the player can find sufficiently high ground, or build a pillar of blocks beneath him or herself, to strike a creeper from above with a melee weapon without the detonation sequence being activated. However, the player should keep in mind that creepers move forwards and to the right (your left) when in pursuit.
Another method to kill a creeper is by doing a critical attack (implemented in the 1.8 update) by jumping in the air and, while falling, quickly hit the creeper. Then attack the creeper again normally. This allows a player to slowly work down a creeper's health while remaining out of the explosion radius.
A diamond sword can quickly dispatch a creeper with three successive hits, one right after the other. This is not a recommended tactic around multiple creepers, though it can be a lifesaver when exploring underground should a creeper suddenly fall down behind the player in dim, tight areas.
If a creeper is below the player, the player can suffocate a creeper (and many other mobs) by placing a block of sand or gravel above the creeper as long as the block they are placing is on a wall or a block in front of the player and above the target mob. It will usually take one to two blocks to cover the creeper and when it is covered, the creeper will slowly suffocate to death. This is a slow way of eliminating a creeper but it will keep the player out of harm's way and preserve the durability of their weapon.
If caught in a difficult place without a weapon, the player can run away if he or she is outdoors or tunnel down towards bedrock and wait for the creeper to de-spawn before surfacing. On singleplayer, one failsafe is to set the difficulty to peaceful, removing all hostile mobs, although this is considered cheating by many players.
A sword enchanted with Knockback is useful for fighting creepers as the player can knock creepers out of countdown range before they can explode. Similarly, players can take advantage of the sprinting knockback to prevent creepers from exploding.
Finally, sometimes letting the Creeper detonate is a viable option, as the range at which it will detonate is slightly larger than the range of the actual explosion, meaning it can explode at a distance at which it will not hurt the player. Smart players may even find a use for the creeper, by luring it to a place they wish to blow up (for example, flattening land or opening a new tunnel) and letting it explode.