Elemental is the name given to the denizens of the three element planes. Each elemental is composed completely of their element, whether it be Earth, Air, or Water, and variations of this cannot occur within their planes. These beings are not derived from elves and dwarves like most of the physical plane and form spontaneously within the swirl of raw element energy.
These beings are effectively immortal within their own planes and the oldest are known as Ancients. Their minds differ from humans and their thoughts are strange. They are part of and yet separate from the creation of the physical plane, germinating in the elements themselves rather than being created by the Steward or his servants.
Only a fraction of their kind took note of humans until recently, acting as spirit guides to shamans and sometimes leaving their traces in the Spirit World through dreams. How exactly they do this is unclear, though the some shamans believe that elementals can follow their own element wherever it goes. In the days leading up to the Apocalypse, many elementals were drawn through the veil between the planes and were destroyed as a result of direct conveyance, so few now love humanity.
The birth of an elemental is akin to the birth of a Sphere of Order. Within the vast churn of the element plane there are moments when the constant change is halted and a pocket of element is able to maintain its form. If it lasts long enough, it is detected by other elementals who find and nurture it. The young elemental develops sentience and learns to maintain its own form.
As mentioned above, elementals do not die naturally on their own planes. Some choose, after any amount of time, to relax their grip on ordered form and return their energy to the plane itself. This is usually done quietly and with little fanfare. All elementals know that when they do this, the essence that was once them will eventually become part of another elemental or sent to the physical plane to reside there a while within another substance or organism. The only way to truly destroy an elemental is with Fire. A pure elemental is dry tinder to Fire and it consumes them completely, ensuring that their essence is removed forever from the rest of their kind.
The overlapping of the element and physical planes during the Apocalypse allowed for hybrid elementals to form, but these are not natural and are generally shunned by pure elementals. Hybrid elementals are also not as utterly vulnerable to Fire as pure ones, though it still damages them massively and will eventually consume them. There are any number of examples of these, most unique, but broad categories are as follows: Mud (Earth and Water), Sand (Earth and Air), and Ice/Steam (Water and Air).