Geoffrey Fettel is Paxton Fettel's older brother, they share the role of leading the Pantheon - their peers in the Enrichment Center's genetic engineering program, known as Origin.

As part of the Origin program, Geoff was among the earliest births. He and his brother Paxton weren't originally 'planned' but once their primary male donor, Wilson Carver, got on board, they were eagerly designed and implanted. Unfortunately, of course, their primary female donor was Alma Wade. The same Alma that Keenan Lane had pegged as his 'weapon' against Ulathoi. Alma had never been the most stable of individuals, and thus her children were somewhat expected to be in need of serious training and molding. In Geoff's case, that never proved necessary. Paxton and Geoff share four of their six respective donors - Alma and Wilson being the bulk (at over 65% of their genetic makeup) but the two which he and his brother don't share clearly shaped each of their specific power sets and subtle changes to their appearances.

Geoff is just about one full year older than Paxton. Geoff's birth was marked with a fervent anger and a lot of destructive Vortal power being thrown around by his mother. Paxton's, however, was calm, smooth and almost uneventful. The reasons for this eluded the scientists but not the boys: Paxton allowed Alma 'in', while Geoff was a blank to her. Alma wanted to hold her child, knew that her father Harlan would never allow it - Harlan never referred to his own grandsons as such, and even refrained from calling Alma his daughter.

Geoff takes greatly after Wilson in both appearance and abilities. Both are tall, strongly built, and somewhat hirsuit. His hair is the same shade of a rich brown-black, Geoff's is shaggy and usually kept around shoulder-length. Geoff's eyes, like Paxton's, are a pale grey blue shade quite unlike their father's side of the family - both are their mother's color to an extent. Geoff's skin is slightly swarthy, his nose a little longer, and lips a bit fuller than Paxton's. But there was never any denying that they were closely related, to look at them. They appear as two sides of the same coin: Geoff the 'strong' one, and Paxton the 'smart' one - but never ever let it be said that Geoff is anything less than smart. His intelligence shows in very different ways than Paxton's, specifically his use of tactics and quick adaptation to situations.

To boost his potential and carry on the experiment that had been started decades before, Geoff and his brother both were treated with the Icarus process which served in Geoff's case to give him immense strength, durability and speed. He can literally see bullets and dodge them by moving out of their way. He's been known to be able to shoot rounds out of the air.

His Vortal prowess was never remarkably apparent, Armacham's testing showed erroneously that he and Paxton were not telepathically connected - that couldn't be farther from the truth. Geoff's mind is incredibly durable and strong, like his body, and even their mother Alma cannot 'see into' his mind. Truth be told: even Keenan can't easily read Geoff's mind, and that's saying a lot. Geoff and Paxton shared most of their early years intimately, their entire past up until about age eight was almost inseparably one memory. Geoff refers to those times and his brother in a strange format: "Paxton-the-mind, Paxton-my-brother, Paxton-the-boy".

Because Alma was quite clearly insane, steps had to be taken to ensure that she didn't damage too many of the children in the Enrichment Center where she herself, even as an adult, had been kept. But from her Vault - a sturdy stand-alone cube suspended in the eastern wing of the Center and watched over by the complicated AI called GLADOS (Genetic Latency Aggression Deterrence / Observation System) - Alma could still find her own family members' minds. She delighted in torturing Paxton, because his mind was so very open. Paxton, as a very young child, sought refuge and for a time, his brother's mind provided that refuge. His ability to simply 'be dark' to Alma withstood a lot of her invasive efforts, but still they couldn't be 'one' all the time. When Paxton finally succumbed to Alma's controls, murdering a scientist and causing Pax's mind to retreat, Geoff found that he could no longer really 'trust' that level of intimacy, and Pax's safe warm mouse-nest threatened to burn him from the inside out.

Melissa took over the duties of protecting Paxton from his mother after the second incident, to Geoff's great relief. However, that didn't mean that their connection was in any way severed: far from it, it simply meant that they adapted a more subdle link that Alma could not track. To Geoff, this progression was natural and easy. Though he's a bit rough seeming, Geoff is reasonably kind and thoughtful - he takes everyone's needs into account, as much as he can, in order to best serve their needs.

As a pair, they were originally intended to be sold off or 'rented out' as warriors - but Paxton mastered his cloned troops and became known as the 'leader' type, while Geoff retained his status as a gloriously talented warrior. Both of them have always neen well suited to those roles, and if Geoff was ever jealous of his brother's status as the 'star' pupil, he never showed it. It's unlikely he ever really was, Geoff has always been comfortable with his position.

Though Paxton is far more outgoing and overtly responsive to people around him, Geoff is still quite charismatic in his own quiet way. It was possibly that quiet, calm nature that drew Isabella Wong to his side - though they were both rather young, and she two years older, they became known as 'a thing' for some time before her departure. Geoff and Bella might have looked an unlikely couple, but obviously they still had more than enough to talk about and ponder. Isabella's rash decision to head past the Vault that got her nearly killed deeply bothered Geoff, he clung by her side as she was being healed; and though he didn't defend her actions specifically or verbally, he quietly reminded his brother that her actions did have the end results they needed to achieve. (Melissa loudly reminded him of that very same thing.)

When Isabella left the Enrichment Center, Geoff became very withdrawn and more moody than he had been before (which is kind of saying something, because he always looked withdrawn and moody). To counter this, and to allow them to fully exploit their new teleportation system connecting the Center with Black Mesa, Melissa and Paxton cornered Geoff and went to Black Mesa for a day or so. It was while they travelled that Paxton became suddenly aware of his own connection to the Mystery's world of Xen, and Geoff and he solidified their own relationship once more. Paxton was, apparently, dead-set on not falling into Keenan and Wilson's 'trap' of activities - and for several years, Pax did so not by openly forging his own direction, but instead by following his pathfinder brother's lead. Geoff knew that this would ultimately fail, but he also has always allowed his brother to make his own mistakes.

Many of the Pantheon, by that time ranging in age from 14 to 21, had already settled among the Black Mesa population, preferring to remain in a stable environment rather than the dangerous Outlands near City 47, their home near Atlanta, Georgia. Geoff still scouted, scavenged and hunted down both Armacham soldiers and later Combine units for quite a while, keeping things safe around the Icarus and Medusa facilities. Eventually, Paxton did accept his role as the Mystery's heir, and at that same time, Geoff realized that his true love had been staring him in the face for years: Alyx Vance, daughter of Eli Vance, extraordinary 'normal' student at the Center. He feels the need to keep her out of trouble - a difficult task given her penchant for finding it. Alyx also winds up helping discover information relevant to their errant Pantheon member, Isabella.

Geoff's relaxed attitude had always carried him through unusual events, so the birth of his niece Darly hardly dented his plans to help retrieve Bella and get an established foothold in other parts of the world, to aid the defeat of Ulathoi. He and Alyx along with a number of others head to Europe during this time, and he's finally reunited with Bella. She's a bit worse for wear, and thus it's actually his idea to have her placed into stasis for her own good. When Paxton finally did have to go looking for Alma, Geoff's role as the Pantheon's leader was more sharply defined, but less necessary.

During their stay in Europe, Geoff is able to help establish numerous outposts for refugees that live in the Outlands between each of the now-dwindling Cities, including Wilson's Norway home - a nice place, complete with a neighborhood and protective shielding once Alyx is done. It is there that they occasionally retire, and a direct line exists between the Convocation supergroup's base, and that home now.

Geoff and his brother do not always get along, though Paxton is well aware of what might happen if he truly angered the bigger, stronger man. Geoff has shown that he, like Wilson, has a tremendous amount of strength but also the willpower not to use it haphazardly, as well as the sheer speed and dexterity to avoid any serious injuries if he wishes to only spar. In that regard too, Wilson remains a bit jealous of his sons - both of them, not just Paxton's spot as the Mystery's heir. Had Wilson gotten the benefits of being born rather than grown, and had he experienced his strength in a way that would allow him to hold it back - like Geoff can - he feels that he might have been of more use. But Geoff and Wilson also relish their amazing strength and often have competitions at Black Mesa: throwing rubble around and clearing hallways, while their assorted 'fan club' of women watch.

While his strength and command are always appreciated, they're not always required. And aside from that throwing around of rubble and assistance with the reconstruction of things at Black Mesa after Ulathoi was defeated, Geoff - like others - grew somewhat bored. Having himself placed in stasis on a reasonably frequent basis means that he didn't miss "the good stuff", and didn't feel like he wasn't of any use otherwise. He enjoys being in Paragon, allowed to really let himself loose.