There are three kinds of Walkers that exist, or are said to exist on Solterra. What they have in common is that they are extremely powerful, and often have motivations and desires that are incomprehensable to Gryphs in general. They usually wear a Gryph like form, but many of them can change shapes apparently at will, at least that's what the myths say. Where myth and reality divide with these can be hard to tell as many can go their entire life, or areas can go generations without seeing one.
Better known as Demons, Earth Walkers can fairly conclusively said to exist. They usually superficially appear to be Gryphs with fantastic attributes. They tend to be very physically powerful, but are often emotionally unstable in one way or another. They walk Solterra, and do what they will for the most part. Despite their power they rarely make their way to groups of Gryphs on purpose. In history there are tales of them taking over cities with their great individual power, but it doesn't seem to be something that happens regularly. These creatures of great power can rock the earth, cause fire to blossom unprompted, and tidal waves to rise up. They should not be underestimated, and nor should they automatically be assumed to be good, bad, or anything else. Each is different and should be approached with caution.
Dream Walkers are harder to be certain of the existance of because of their venue of interaction. They appear to have the capacity to be in, and manipulate the dreams of Gryphs. It is said that when you wake up from the most tantilizing, most vivid dreams of your life, but the memories fade within seconds that you have interacted with a Dream Walker. Some believe that Dream Walkers are related to Vulpines because of the role of Brother Fox in the creation of the world. It is fairly clear that most Dream Walkers are benevolent, but there are rumors of some that can be harmful. Those potential threats that only legends speak of are why we teach our children that if you die in a dream, you die in real life, and how to wake up from a dream just to be sure. There are myths of a few darker Dream Walkers that fed on the lifeforces of others through their dreams, sustaining themselves for milinea. Most consider these stories myths only, but it is better to be careful.
To some these are simply mythology and the religious figures that are accepted in the standard beliefs of Solterra. Others believe that the religious figures are based on the very real Void Walkers. It is difficult to say if they do or don't exist beyond debate though because it is said that they walk the stars, and are rare. Some keen eyed Gryphs watch the skies and point to errant stars moving across the night sky with no pattern, or shooting stars as evidence of Void Walkers. Accounts of what are believed to be Void Walkers are generally regarded as simply stories, but those that believe in them keep watching for them.