Common noun:
* When referring to any group of people who were Scandinavian seafaring warriors and traders during the Viking Age (8th to 11th centuries).
* Example: "The Vikings were known for their longships and raids."
Proper noun:
* When referring to a specific group of Vikings, such as the Vikings from a particular region or a particular historical period.
* Example: "The Vikings of Denmark were fierce warriors."
* Also, when referring to the historical period itself.
* Example: "The Vikings era saw significant cultural exchange."
In the context of the TV show "Vikings," it is a proper noun, as it refers to a specific show.
It's important to consider the context and the intended meaning to determine whether "Vikings" is functioning as a common or proper noun.