John Smith (Earth-5875)

"It's a big, bad universe, Sergeant. Covenant aren't the worst of it. You've done what you thought was necessary for the greater good. And so have I."

- - Major John Smith to Sergeant Zhao Heng Lopez

Major John Smith was a senior officer of the Office of Naval Intelligence Section Three, where he served as a scientist.

Mona Lisa incident
In October 2552, Major John Smith and his science team of the Office of Naval Intelligence Section Three took control of the prison ship Mona Lisa, hoping to use it as a makeshift laboratory to study the endoparasictic sapient species known as the xenomorphs in an attempt to weaponize them to fight the Covenant, following the failed classified mission undertaken by Major Michael Bishop to Fiorina 161 in August of the same year. Once he boarded the ship, the ONI agents performed a slipspace jump to the Soell system, where they located the wreckage of Installation 04 and captured Ovomorphs to bring aboard the ship.

Smith then used human and sangheili prisoners as hosts to the xenomorphs in order to test the capabilities of the species. The xenomorphs, however, were easily able to overrun the ship, prompting Smith to remotely launch most of the Mona Lisa's escape shuttles to escape to prevent the xenomorphs from escaping. While he initially tried to go the the freighter's bridge to initiate its self-destruction, he was overrun and was forced to lock himself into a sealed panic room. There he remained, until Smith was found by Sergeant Zhao Heng Lopez and some of her UNSC Marines. Smith claimed to be the medical officer of the Mona Lisa, and insisted they should leave the ship at once. However, Lopez suspected about him and ignored his pleas, revealing they would self destruct the ship as per the Cole Protocol.

Once they came across a xenomorph growth, Lopez questioned about their nature to Smith, who claimed it was a Covenant virus that had affected the human prisoners. They were later attacked by a group of Facehuggers, but managed to kill them. Lopez then hit Smith, realizing he was lying, and had Kwaku Mahmoud search him througly, where he found Smith's ID badge, who revealed his identity as an ONI agent. He outranked the Marines, however, and ordered them to flee from the ship, but Lopez refused to leave her men and women behind. Betraying the soldiers, Smith drew a concealed knife and stabbed Mahmoud in the neck, killing him and stealing his M41A pulse rifle before escaping from the room.

He was then able to steal Karina Burgundy's D77-TC Pelican in the Mona Lisa's cargo bay and escape to the UNSC Red Horse. While approaching the Red Horse, he drew the attention of a Covenant ship arriving in the system, forcing Commander Tobias Foucault to destroy the Mona Lisa with a Shiva-class nuclear missile to ensure the xenomorphs would not escape and spread, but this in turn the doomed the Marine survivors.

Once he arrived in the Horse, Smith was detained by Foucault, who planned to have him court-martialed for his crimes against humanity.