What is the significance of the Spirit of Vengeance in the Ghost Rider mythology?

The Spirit of Vengeance, often embodied by Zarathos, is the core of the Ghost Rider's power and purpose. It's an ancient, cosmic entity dedicated to punishing the wicked. The host (like Johnny Blaze) acts as a vessel for this spirit, channeling its power and carrying out its mission of retribution. The host's struggle to control the Spirit is a key element of the character's complexity.