Chakas was an ancient human born on Erde-Tyrene after the end of the Human-Forerunner Wars and the devolution of humans to that of a more primitive ancestor. He, along with his friend Riser, worked with the Forerunner Bornstellar (who later became the IsoDidact) on Erde-Tyrene to resurrect the Didact from his cryptum, and following that, traveled with all three through the galaxy until their capture by the Master Builder near Janjur Qom.
Chakas and Riser were deposited onto Zeta Halo by the Master Builder in the aftermath of their capture, where they were forced to fight against the Primordial and Mendicant Bias for control of the ring. During that encounter, the geas of Chakas was revealed to be the Lord of Admirals, the commander of ancient humanity during the Human-Forerunner Wars. He, with the help of the IsoDidact who arrived to take command of the halo, successfully stopped the Primordial and disassembled Mendicant Bias.
Though Chakas survived the battle, he was so disfigured by the encounter that his body could not be saved. In an act of kindness, the IsoDidact saved his mind, implanting it into a Forerunner monitor carapace and later naming him 343 Guilty Spark. Though still Chakas at heart, Spark’s memories were compartmentalized, forgetting his past for the next one-hundred thousand years. In 2554, two years after the firing of Installation 08 over the Ark, a severely damaged and partially decompartmentalized 343 Guilty Spark made contact with an ONI team aboard the UNSC Rubicon and proceeded to commandeer their ship for his own purposes. Three years later Chakas, now going by Spark, was discovered by a salvaging team led by Rion Forge and made part of their crew, assisting in the search for the remains of the UNSC Spirit of Fire.