Born in November of 2485, Corey was a standard child who performed well in school and made many friends. One of his greatest skills was keeping his secrets and finding out the hidden information other had wished to keep hidden.
In the year 2505, at the age of 20, Corey volunteered, and was accepted, for the Orion Program, and would serve the UNSC for years to come. Only a few years later, the Office of Naval Intelligence cam to him with an offer to join their ranks within Section III. Corey accepted this offer, and he was assigned to his partner, Petya Hass, another ORION soldier.
In 2516, at the age of 31, Corey married to his wife Itzal Tamaya. The next year, in April of 2517, they had their only son, Ivan Sinitsin. Ivan was subject to testing and had to be given specially formulated injections to ensure no birth defects. Due to Corey's continued allegence to ONI, he complied when some the offspring of ORION soldiers were being taken, in return of assurance that none of the tests on Ivan fould be harmful to his health.
Itzal refused to cooperate, and had threatened to expose what she knew about the abduction of what would become known as Spartan I.Is, which Corey admitted was more than she should have know about his work. Due to this threat, ONI had Itzal killed and Corey's operational partner, Petya Hass worked with Corey to cover up her death and watch over Corey to ensure he wouldn't make the same mistake again, and inadvertently doubled as Ivan's mother.
Years later, when the Covenant attacked Harvest, Corey and his friend Joe both were both deployed to the planet, where only a year later, Corey was said to have died. Petya stayed on Arcadia with Ivan, both working as an agent on Arcadia, and as Ivan's mother, through which Ivan was an experiment of ONI. Corey and Petya would not again work together until 2531, when the Covenant attacked Arcadia and Petya is believed to have died.
They would continue to work together until the year 2553, when the trade of a forerunner artifact from an outer colony to the UNSC goes south, several members of both sides being killed in an insurrectionist attack to prevent the artifact from being transferred. After this, the colony stated it would keep the artifact, due to the overwhelming population that wanted it to be that way.
Corey was deployed to begin a false insurrection, one that would overwhelm the colony's military, and once it had, he would intentionally lead the insurrection to failure, against the UNSC as they try to re-take the planet. Unexpectedly, the colony manged to hold back the Corey's forces in a state of perpetual war, Corey even making his force more similar to that of terrorists to attempt to weaken the enemy.
It is suspected that sometime during this conflict that Corey had become mentally unstable, a common side effect in ORION soldiers and not surprising given his countless years of war. It's believed that he had abandoned the mission and was leading the terrorist insurrection out of hatred for the UNSC and ONI for what they had done to him and his family.
During the war, Corey learns that one of the major combatants, and one of the colonies more iconic soldiers, is his son, Ivan. A few years later, when the war is considered over, and Ivan had relocated to another outer colony called Trost, He followed him there. Corey knew the best way to ensure he and his some would meet was to threaten innocent lives.
Corey died at the hands of his son in the city of Kairoh on November 1st, 2562. In his death, he covertly gave Ivan a set of coordinates to a hidden location, unknown by ONI. These coordinates were scratched into the inside of the slide of his M1911A1, somewhere he knew his son would in due time. Before he died, he was responsible for nearly a billion deaths, and had personally killed over 300 people.