The wolf has 3 behavior modes, wild, hostile, and tamed. Each has a specific way of making the wolf act and interact with you and other mobs. They spawn as wild, will turn hostile once attacked, and tamed once given bones. They generally spawn in groups up to 8.
In the wild mode, the wolf does not attack you. It will however attack sheep. This is the default mode they spawn in. Furthermore, when they spawn they spawn only in Taiga and Forest biomes, and in packs of 1-8.
In the hostile mode the wolf will attack the player, but will only turn hostile after being attacked. Luckily they are very weak and only deal a hearts worth of damage, and a heart and a half of health. If being chased by a pack, one trick you can use is to jump off a cliff if you have 7+ hearts. They will die from the fall damage but you will live. This is only recommended if the entire pack is chasing you, and you could risk death if they all attacked you at once.
The final mode is tamed, and the wolf then becomes the only ally mob in the game. It will fight for you, and will remain seated so it doesn't follow you if you right click it. But, if it is seating while you are attacked it will then try to help you. Most people tend to keep their wolves in their houses because they die very easily and can get in your way while mining, breaking dirt, woodcutting etc.
