The Ice Wolf is one of the main monsters of the Icy Land.
Icewolves are attracted to Heat. They generally track the player as the player generates heat, however it can get confused by other heat sources like Bonfires or leftover heat from the player standing still. Orb of Winter will actually repel Icewolves.
Icewolves will only move through Icy Land, Blizzard, or Cocytus, as those are the only three lands with the temperature mechanics. If you're pursued by an Icewolf and leave the land, they will generally track your heat trail to its end and then block that entrance to their land indefinitely.
If an Icewolf enters the Volcanic Wasteland, it will turn into a red Lava Wolf; however, Lava Wolves will not re-enter the Icy Land.