The all-hating personification of destruction and suffering, in Manichaeism he is a Demiurgic Anti-God associated with Satan, Mara, and Ahriman. In Jungian Gnostic alchemy, he is Abrasax, the devil associated with the Demiurge and the Collective Consciousness. In Tarot, he is The Devil, known as Set-hen, Saturn, and Adonai, who rules material passions. He's also called the great deceiver, the father of lies, and the illusion. It is this latter sense that I have some insight to shed on the matter. As children, most of what we experience is novel. We are seeing the world through clean eyes. As we grow older, we learn to process visual information by comparing it with what we know. This means that kids process visual information slower, but in more detail, and can remember more about what they see than adults, who generalize what they see. For instance, an adult might look into a room and remember that there's a chair in it. A child might look into the same room and remember the colors of the walls, the direction and color of the wood grain on the chair, etc. They take in more of the "raw experience" and see "things-of-themselves" rather than categorizing those experiences as a chair. On top of this, the kid experiences novelty, whereas the adult has seen plenty of chairs in the past. This illusion of abstract concepts formed by comparing the past to the present, prioritized over the undiluted sensory experience, leads to the adult no longer finding enjoyment in the moment of something so mundane. The lie of the concept of what a chair is comes before actually seeing this specific chair as it is in that moment. This is, potentially, why Buddha-nature is often described as neither existing nor not existing. It's seeing beyond the abstract concepts of the labels we construct and seeing things as they are rather than how we define them or the context that they might be in. This happens with more than just vision. As a kid, you might enjoy terrible candies and poorly made cartoons, only to be hyper-critical of them when you age and have a broader understanding of food and entertainment to judge them by. This in-the-moment novelty has a downside for kids, too. Horror movies are scarier. Papercuts and bruises feel more painful. An argument with a friend can feel like the end of the world. In adulthood, these are less pressing obstacles, in part because of the broader perspective gained from experience. It's also possible, with time, to learn self-discipline and integration, making even worse hardships easier to endure. This is also done, in part, by letting go of the analytical mind, and refusing to label emotions or sensations as "bad" so that one can accept their experience of them in the moment. While we cannot be purified of these illusions entirely, as some amount of abstraction and contextualization is necessary for daily functioning, we can learn to recognize them for what they are and take control over them rather than let them rule over or torment us. But those are just the thoughts of a young fool, really, and maybe a bit lengthy. This personification of evil is one that has been on my mind a lot lately as I struggle with my own inner demons that beckon me towards being miserable, causing misery, being self-destructive, and tearing down others. By gaining a better understanding of these impulses in myself, I have been able to overcome them. That's why the devil in Manichaeism is also known as the "evil impulse" (Yetzer Hara) or the "malevolent mind" (Angra Mainyu); it is that inner demon. It can only be guarded against by facing it and understanding its tricks.