Wolf

Wolves are neutral mobs that can be found roaming around forests and are often together in packs. They were added in 0.9.0.

Taming
Wolves can be tamed by being feeding them Bones, which can be obtained by killing Skeletons. Taming can be done by getting close to them and then holding the screen for a few seconds or by clicking the "Tame" button (works only when close). You can tell if its successfully tamed when: Wolves can help you fight against some other player or a hostile mob, so they're well worth the taming.
 * Hearts appear after giving the bones they want.
 * The red collar appears.

Wild
Wild wolves spawn in Taiga, Plains and Forest biomes. The pack wanders aimlessly, but they sometimes coordinate and kill sheep. After in water, wolves shake itself dry. Wild wolves turn hostile towards the player if attacked, and so will the pack.

Tamed
Once tamed, a wolf will follow the player wherever they go. It will shake itself dry whenever it reaches land after a swim in water. Tamed wolves teleport towards the player if they are too far, except when the player is currently flying. Tamed wolves are useful because when a hostile mob or another player attacks their owner, the wolves strike back. When the player hits a mob, they will attack said mob. You can make them sit or stand by going close to one of them and tapping the sit or stand button.

Combat
Tamed Wolves will attack any mob the player attacks, and will attempt to kill it. Tamed Wolves can easily defeat Skeletons, and Zombies, but struggles a bit against spiders. It is a bad choice against Creepers, as unlike PC, wolves will attack creepers, and a creeper can explode, instantly killing or critically injuring it.

Trivia

 * In early 0.9.0 beta builds, tamed wolves had a black collar.
 * Hostile wolves will make growling sounds at the player.
 * Some players prefer to call tamed wolves 'dogs'.
 * Wolves may enter love mode while sitting, but cannot breed till made to stand.
 * When on LAN, attacking another person's dog will cause it to chase you. Even when sitting, it will leap towards you.