Callisto is the first Human man, the son of Maya the Aldar after Maya's rape by the Unnamable Horror. His twin sister, Sinope, is the first human woman. All members of the human race are ultimately descended from the coupling of these two.
Callisto, along with his sister and lover Sinope, possessed the immortal lifespans of the Aldar. The descendants of Callisto, however, gradually phased out from their immortal state to mortality. Lucretius, God of Knowledge, had predicted this as the inevitable result of interbreeding pure Chaos with an Aldar--the entropic energy of Chaos would gradually cause the Aldar energy to deteriorate over time.
While Callisto was on a hunting trip, his son Anake killed Sinope in her sleep, an event that would become known as Anake's Passion. 50 years later, in a rage inspired by the schemes of Thoth and Shaitan, Callisto sought revenge for Sinope's death and murdered the sleeping Anake. Callisto then became entrenched in his own insanity.
Callisto perished at the hands of his grandchildren, Rukal and Lakspura.