VGFacts

The Heartless boss in the Frozen world, Arendelle, is actually based on the Norse Mythological figure "Skoll". In the Myths and lore Hati and Skoll are two Wolf deities who try to "eat" and "chase" the moon and sun respectively thus creating day and night!

Here is a description of the Norse figures:
https://norse-mythology.org/skoll-hati/

Here is the Boss Battle:
https://www.youtube.com/watch?v=REEWg_Qdw-g