Planeswalkers are Astrals who are born with the gift of the elements. The first of the Planeswalkers was Lucius who wields the element of darkness up until Veltrex, wielder of light, was born.
Each Planeswalker also wields their own unique weapon crafted from the elements themselves.
Origin
No one really knows how they gained elemental powers at birth and even why they did. Some speculate that their souls were infused with elemental power by Tyg for the sole purpose to guard over Terrahypt more efficiently. This however, worked to no avail, as there seemed to be no purpose for them being there due to the fact that normal Astrals seem to be efficient enough of defending Terrahypt as well as they do without their elemental powers.
It was until the war against Aeon that they realized their purpose.
Aeon appeared to be too strong for any other Astral to fight it. Every Astral that fought the entity was killed in combat and then absorbed into its body.
When the Planeswalkers faced Aeon however, their elemental powers seemed to shield them from some of Aeon's powers allowing them to have a fair chance at fighting the entity.
Wielders
Veltrex - The brilliance of Helios (Wielder of Light) "Greatsword"
Lucius - The growing shadow (Wielder of Darkness) "Scythe"
Magmaul - The raging inferno (Wielder of Fire) "Battle axe"
Spire - The shaking tremor (Wielder of Earth) "Warhammer"
Rift - The great typhoon (Wielder of Wind) "Tomahawk"
Maelstrom - The roaring tsunami (Wielder of Water) "Trident"
Bifrost - The great avalanche (Wielder of Ice) "Mace"
Diminish - The flashing strike (Wielder of Thunder) "Staff"