Primordials stand outside of Creation. They are creatures of chaos and entropy, formed at the borders between the havens or Creation and the primordial chaos. They have absorbed just enough order to maintain a physical form, rather than being swallowed up by the chaos, but they are by their nature chaotic. Like chaos, they both create and destroy. They are not necessarily evil, and are no more likely to be cruel than any other creature, although with their penchant for frequent destruction they can be perceived as such.
Some Primodials came to being inside of Creation. Some were bound to the earth by Immortals, but other roam free. It can sometimes be difficult to distinguish between a Primordial and an unseelie fey, and indeed the distinction may be a continuum depending upon how much of them is made up of the order of Creation, and how much is primordial chaos. But in general, Primordials are not limited to story logic, and if they have an agenda at all, it is likely to be in furtherance of bringing about a state of entropy. Some are motivated, for reasons they neither understand nor care to understand, to bring about an end to Creation, and reunite with the chaos. Others simply revel in the destructive forces of nature, like storms, earthquakes or volcanoes. Or in forces that both create and destroy, like tides and rivers.
Whatever their motivation or alignment, Primordials are universally dangerous and powerful.