The Winter Wolf, also known as the FrWOLF in the Nintendo Entertainment System version, is an enemy in the original Final Fantasy. Winter Wolves are the toughest of the wolf family, but they are very weak due to having zero Defense, making physical attacks extra powerful, not to mention having an elemental weakness to Fire. Given that they appear with other Ice-type monsters, a single Fira can easily defeat an entire group.
On the other hand, however, they are also extremely dangerous for the unprepared. Winter Wolves have a special attack called Icestorm, which deals Ice damage to all the party members. Despite its low damage, the fact that Winter Wolves tend to appear in gigantic packs more than makes up for this, and a party that isn't quite ready can quickly lose 200 or more HP a round to a group of Winter Wolves. NulFrost - and taking the wolves out quickly - can cut down the damage they deal.
They appear as random encounters in the Cavern of Ice, attacking in large packs or along with a lone (or pair of) Ice Gigas. It also appears in the second floor of the Chaos Shrine, and around the cities of Lufenia, Pravoka, and Onrac, which is strange, considering that those are not snowy regions, Lufenia being next to a large desert, and Onrac, next to a tropical river.