Nightcaster Arkvarius was a half-Anodite, half-Oneiromancer from a destroyed planet in another galaxy.
He appeared only in a flashback in Hit and Miss.
When Azmuth was a young legendary warrior, Nightcaster sought out the destruction of the legend solely to prevent the Omnitrix from ever being created. After an unforeseen incident, Azmuth managed to defeat him using a new weapon Azmuth "found." He teleported away and was presumably never seen again, by Azmuth at least.
At some point during his life, he moved to Ledger Domain and asexually birthed Murmadan Arkvarius and Nightcaster Arkvarius II. Sometime before or after this, he imprisoned Zyzz Vyva, an alien who warred against the population of Ledger Domain, in an underwater location on Earth.
He passed away some time after imprisoning Zyzz, passing on his legacy to defeat Azmuth to his youngest son, Nightcaster II, who unbeknownst to Azmuth was taking on the alias of the original Nightcaster.
- In Hit and Miss, he appeared for the first and last time to a young warrior Azmuth in a flashback.
- Hit and Miss (first appearance; flashback)