Back Plot (Act 1)
As we know, from Halo 4… John was given a ‘gift’ by the Librarian Imprint. This theorized gift, was initially a resistance to the composer but could be a GEA being unlocked, through speeding up the evolutionary state in John. The GEA in John, could be a possible character mentioned from the Forerunner-Human or Forerunner-Flood Wars. This may have been what Halsey initially saw in her Spartan-II candidates in 2552. Halo has had various mediums(Novels, Comics, Films Series, Collectibles, Video Games) to address the canon stories and history, this has given us a variety of resources to give evidence to John having a certain known Forerunners GEAs.
In Halo Combat Evolved… When John was acquiring the index, 343 Guilty Spark (Chakas) was saying to John “Last time, you asked me, if it were my choice, would I do it? Having had considerable time to ponder your query, my answer has not changed.” This same sentence is what the Iso-Didact(Bornstellar Makes Eternal Lasting) said to Chakas, 100 000 years previously. Quite funny too that John almost activates the ring world and other arrays, thus repeating history(Bornstellar activated Rings via Lesser Ark). [Source: Halo Selentium and Halo CE, Halo CEA]
In Halo 4… When Master Chief is pursuing the Ur-Didact on Requiem and on his Forerunner flagship, Mantles Approach; Chief hears the Ur-Didact voice inside his head, much like how Cortana speaks through John’s armour and neural implants, while different to Cortana as well. When John asks if Cortana can hear the Ur-Didact too, she states their is no activity on the comm channels and she can’t hear anything. This clues a connection between John and the Ur-Didact which is already manifesting…
As everyone knows John’s steadfast companion, through the franchise, is an smart AI named Cortana. Cortana is modeled from a cloned brain from Catherine Elizabeth Halsey. I believe the Librarian has given Elizabeth Halsey GEAs to and so informally giving them to Cortana as well. The only question of who…
In Halo Reach… When Noble Six arrives, to rescue Catherine Elizabeth Halsey, from the invaded ONI Facility, designate Sword Base. Cortana is being finalized in her making process using forerunner artifact to finish her. Noble Six is charged by Halsey, with escorting Cortana’s data chip to Jacob Keyes, captain of the UNSC Pillar of Autumn, a Halycon-class light cruiser. Noble Six successfully completes his mission and Keyes commands Cortana does an emergency slip space, upholding the Cole Protocol. The Pillar of Autumn emergency jump brings them to a Halo Array, Installation 04A. She gathered the information from the forerunner artifact on Reach.
Halo 4… states that Cortana had something done to her by the Librarian Imprint, but she doesn’t know what, a first for Cortana. And when John is being spoken to by the Forerunner Imprint, she states that John and Cortana are an eventuality and that his combat skin, augmentations and AI are a thousand lifetimes of planning.
Many things state that John possesses traits of the Iso-Didact too; when they were young they were rough and rebellious; they both share an involuntary ability to lead their race in times of peril, and in my opinion the Iso-Didact has favor like John with his luck. John constantly prevails, survives and wins; Iso-Didact finds Chakas, Riser and releases the Ur-Didact from his Cryptum, finds what he wants(Precursor Artifact), and later wins the Librarian who favors him for than the Ur-Didact, Wins his arguements in the Forerunner court, Survives in flood space, Doesn’t go mad when he talked to the Primordial.
So my theory is John has GEAs of the Iso-Didact and Cortana/Halsey has GEAs of Librarian. For people who state that a person has to be dead to use them as GEAs where does it states this?