Wolf

Wolves are neutral mobs that can be tamed by feeding them Bones. They were the first tamable mob in the game and were added in Update 0.9.0.

Wild
Wild wolves spawn in Taiga, Plains, and Forest biomes. They wander aimlessly, but will sometimes coordinate and kill sheep.

Aggressive
Wild wolves may turn hostile towards the player if they, or nearby wolves are attacked. Aggressive wolves have red eyes and black patches on their fur. Their tail is also raised slightly higher than wild wolves.

Tamed
Tamed wolves follow the player around the world, and teleport towards the player if they are too far. Tamed wolves shake themselves dry after exiting any body of Water. They can be made to sit and stand by pressing the 'sit' or the 'stand' button respectively. Their collars can be dyed by pressing them with any Dye. By default, the collar is red.

Breeding
Tamed Wolves can be bred using any type of meat, except Fish, if their health is fully restored. When bred, a puppy spawns, which is already tamed.

Wild Wolves cannot be bred till they are tamed.

Combat
Tamed Wolves attack any mob the player attacks, and will attempt to kill it. Wolves can easily kill Skeletons, Zombies and Spiders, but face trouble against Creepers and Endermen, the former due to their explosive power and the latter due to their high health and teleporting ability.

Trivia

 * In early 0.9.0 beta builds, tamed wolves had a black collar.
 * In 0.11.0, the wolves collars are now dyeable.
 * Hostile wolves will make growling sounds at the player.
 * Some players prefer to call tamed wolves 'dogs'.
 * Tamed Wolves may enter love mode while sitting, but cannot breed till made to stand.
 * Before Update 0.10.0, Baby Wolves couldn't swim in deep water.
 * Wild Wolves will have love hearts when fed meat, but will not breed.