Valkyries

"May the Valkyries welcome you, and lead you through Odin’s great battlefield. May they sing your name with love and fury, so that we may hear it rise from the depths of Valhalla... and know that you've taken your rightful place at the table of kings. For a great man has fallen. A warrior. A chieftain. A father. A friend."

- Gobber

The Valkyries are female demi-gods who escort warrior Vikings to Odin's side after they arrive in Valhalla after death. So far they are mentioned only once in the film franchise.

History
Valkyries are Odin's helping spirits, choosing the slain Vikings who are worthy to join him in Valhalla, and later aiding him in the battle of Ragnarok. They are traditionally said to be very beautiful, and even seduce human warriors with their charms. But as they depend on the deaths of mortals for their existence, they can also seen in a sinister light, rumored to sing and dance with glee while surrounded by horrific scenes of carnage.

Dragons: Race to the Edge, Season 5
In the episode "Snotlout's Angels", though not directly addressed, it's suggested that Snotlout thinks he's dead and has arrived in Valhalla, and that the Wingmaidens who greet him when he awakes are Valyries.

How to Train Your Dragon 2
The Valkyries are mentioned during Stoick's funeral, by Gobber.

Trivia

 * It's possible Valka's name was inspired by the Valkyries.