These are fylgjur (pronounced “FILG-yur”) in the plural and fylgja (pronounced “FILG-ya”) in the singular. The fylgja is generally perceived in an animal form by those with second sight, although human fylgjur aren’t unheard-of.
It’s an attendant spirit whose well-being is intimately tied to that of its owner – for example, if the fylgja dies, its owner dies, too. Its character and form are closely connected to the character of its owner; a person of noble birth might have a bear fylgja, a savage and violent person, a wolf, or a gluttonous person, a pig. In a sense, this helping spirit can be seen as the totem of a single person rather than of a group.
Fylgja literally translates as “follower,” but, as often as not, it’s depicted as traveling ahead of its owner, arriving at the intended destination before its owner or appearing in the dreams of someone who will meet the owner the following day. Intriguingly, the term is also applied to the afterbirth, but the connection is mysterious and unclear (Source: Norse Mythology.org)