Right. I've been working on the background for Shepard, and have come up with something I figured I'd run by you guys.
This is actually something I created completely independent of this specific fic idea. The basic concept is an "All-Star Shepard," i.e. one that touches on each of the possible origins for Shepard and weaves together a story out of it. The original story that this was intended for was an unnamed fic idea that I quietly discarded due to a lack of direction (basically, it was the original Mass Effect story turned up to 11. Enemies would be more numerous and angry, like for instance ExoGeni sending assassins after Shepard to cover up the Thorian incident). In order to balance the power, I needed to escalate Shepard's skills and abilities so he could feasably survive two thirds of the galaxy trying to murder him. And thus All-Star Shepard was born.
All-Star Shepard is male (though he could be female; the actual gender isn't important). The background covers all three Pre-Service Histories (<a href='http://masseffect.wikia.com/wiki/Commander_Shepard#Pre-Service_History' target='_blank' rel='nofollow'>Spacer, Colonist, and Earthborn</a>) and combines them into an overarching storyline of Shepard's youth.
Shepard is born on Earth, to parents who were both in the Alliance Military. As a youth, Shepard lived surrounded by petty crime and the underworld gangs that plagued the less well-off parts of the cities. He even participated in some crimes himself. Concerned for their son's future, the Shepards were able to leave Earth by volunteering themselves into an Alliance initiative to protect human colonies in the Fringes. The Shepards and their son left, and arrived on Mindoir, a small border colony in the Attican Traverse, where they would be stationed for the foreseeable future. Shepard was still fairly young, in his middle teens, but he took quickly to colonial life. He enrolled in the local school, made friends, got a job repairing machinery around the colony, and generally cleaned up his act.
Then the Batarian raiders came. The initiative was designed to protect colonies from things like pirate raids, so in theory, they should have been completely prepared for this. However, they were not. The Batarians came in force with numbers and equipment that belied their nature. Pirates are not that well equip, and certainly not that well-organized. Contemporaries would later speculate that the pirates were funded and supplied by the Batarian Hegemony, and sicced on the outer human colonies as petty revenge for human colonization into space that the Batarians saw as theirs.
Whatever the reason, Mindoir was overrun. A distress call was sent out, but not before the Batarians had executed all of the military personnel stationed there, and slaughtered over half of the colony. The rest were rounded up, stripped naked, and examined. Those that 'passed' were branded and were subjected to on the spot cranial implant surgery, without anesthetic, to control them. Those who 'failed' were executed and butchered like animals.
The SSV Einstein was in a neighborhood system, under the command of Shepard's aunt, Hannah Shepard, and was able to pick up the distress call almost immediately. However, when they arrived, they found that their ground forces were unable to advance on the fortified positions that had been erected by the Batarians, due once again to the unexpected preparedness and organization of the Batarians involved. The ground forces were forced to watch helplessly as the colonists were rounded up and treated like animals, men, women, and children alike.
Shepard was one of the few who escaped the carnage. Enraged by slaughter of all of his family and friends, Shepard went on a rampage, fighting back against the Batarians and killing dozens of the slavers with weapons taken from the overrun military base.
However, when the dust all settled, Shepard was one of only colonists left alive and abducted.
Shepard spent several months in deep depression, and was under the care of his Aunt. However, he eventually had an epiphany: he would join the Alliance, just like his parents. He would protect those who couldn't protect themselves. He would stop this from ever happening again.
On his eighteenth birthday, Shepard signed up, and was shipped off to basic the next day.
So that's the beginning. Now we get to the Psychological Profile. Once again, it's a combination of all three of your canonical choices. This is where it gets a little bit complicated, so stay with me on this.
Several years after joining the Alliance military, Shepard was on a mission under the command of Major Kyle on Torfan. The objective was to break into and destroy a batarian pirate base that had been staging raids on nearby colonies. Shepard would serve as the scout, moving ahead and sending back reports on enemy locations and strengths. Kyle would lead the rest of the unit in behind, using Shepard's data to rout the pirates.
Unfortuately, few well-laid plans survive contact with the enemy. Seeing through the unit's attempts at stealth, the batarians deployed a newly developed chemical weapon specifically intended to be used on slave raids. It caused severe hallucinegnic reactions in humans, rendering them confused and disorientated, while having no affect at all on batarians. Not expecting a gas based attack of any sort, the entire squad was caught unawares and subjected to the chemical. However, the chemical soon proved to be a double-edged sword: though it had tested well against slaves, it had never been used against trained soldiers before. Shepard, once exposed, went berserk, and began killing every batarian he saw, regardless of whether or not they were pirates, workers, scientists, or whether they were attacking him, running away, or surrendering. Kyle, in the mean time, began issuing increasingly reckless and illogical orders to his squad, commanding them to split up, search and destroy, try to find and rescue Shepard, fall back, and continue onwards to the objective.
By the time all had been said and done, the pirate base had indeed been eradicated. However, over two-thirds of the original force had been killed due to a combination of reckless orders and unreliable data sent back by Shepard.
Someone had to take the fall. Kyle was a well-respected and highly decorated commanding officer. Shepard was a nobody, still green around the edges. The choice was obvious. The Alliance brass hung Shepard out to dry, pinning the majority of the blame on him. They cited psychological trauma from the events on Mindoir, said that it was his faulty data that caused the unit to stumble into the gas, and claimed an unsuitability to lead or be lead. Though other, more level heads in the Systems Alliance were able to ultimately prevail and get Shepard off with a mere slap on the wrist, the nickname "Butcher of Torfan" stuck, as did a reputation for being cold, calculating, brutal, and ruthless.
Later that year, Akuze was in the early stages of colonization by humans when all contact was lost with the pioneer team. The Alliance sent in Shepard's Marine unit to investigate and look for survivors. When the unit camped for the night, they found themselves set upon by Thresher Maws. The Marines had no idea what they were facing and almost the entire unit was killed, with fifty marines KIA by the final count. Shepard was, as you can probably guess, the only survivor. Trapped in a hostile enviroment on an alien world without any way to escape or signal for help, he was forced to overcome physical and psychological trauma that would have broken most people. He survived when everyone else died, and was the only one left to rescue when the Alliance sent in a second team in to investigate.
Admiral Hackett, aware of the dirty politics over the debacle on Torfan and an old friend of Shepard's family, arranged for nearly a year of full-paid leave for Shepard, so that he could recover from his ordeal on Akuze in relative peace. In Hackett's own words, "you need a vacation and you're going to get one, even if I have to strap you in a chair myself."
However, that was sadly not to be. Echoing events from years earlier, the planet Shepard was on leave on, Elysium, was attacked by an army of Batarian slavers, pirates, raiders, and warlords in an event known as the Skyllian Blitz. Coordinated by crime lords who were being openly funded by the Batarian Hegemony, it was an attack that the batarians spun as "just retribution" for both human expansion into the Skyllian Verge, and for Alliance initatives to crack down on slavers and pirates, which they viewed as trespasses on their cultural rights.
However, what the Batarians didn't count on was a large number of Alliance personel who were on leave on Elysium at the time, including one Lieutenant Commander John Shepard. In an incredible display of heroics and leadership, Shepard rallied the various civilians and military personnel into a coherent fighting force, and held their ground against the overwhelming enemy forces while the Alliance Navy, including the SSV Agincourt where Navigator Pressley was stationed at the time, cut through the attacking pirate fleets in the skies above. Ultimately, the day was won, due in large part to Shepard's courage and nerve in risking his own life to save his fellow soldiers and lead a charge against the invaders.
For his incredible bravery and actions far beyond the call of duty, Lieutenant Commander John Shepard was awareded the Star of Terra, the highest and most prestigious honor the Systems Alliance can award an individual.
In light of Shepard's accomplishments, and using the sudden upsurge in Shepard's popularity amongst the Alliance brass for his efforts on Elysium, Hackett pulled some strings and got Shepard enrolled into an elite special operatives program known only by it's code designation within the Alliance heirarchy: "N." Not only would help Shepard's career, but it would also insulate him almost completely from the whims of Alliance politics, because much like Spectres, soldiers who are designated N have all of their missions and actions sealed and classified. It would be almost impossible for the Alliance to crucify Shepard again; as an N agent, he would be almost untouchable.
According to canon, N is a highly elite and covert branch of the Alliance military. They are the absolute best of the best, and are divided into seven different levels, with each higher number designating a greater amount of skill, proficency, and training. Amongst them, the N7 are the most skilled, most talented, and most highly trained. They are the absolute best that the Systems Alliance has to offer. Their calling card is their rank, N plus their number, and the red bar symbolizes both their status as commanding officers and the blood that Systems Alliance has, and will continue to, shed in the mission to protect the innocent and colonize the stars.
Shepard, of course, rose through the ranks quickly, mastering the various skills and techniques necessary, and becoming proficient in every area that was expected: hacking, data retrieval, infiltration, assassination, assault, full-spectrum weapons training, and even biotic manipulation were all covered, and each one was mastered in its own turn. In less than a year, Shepard had risen to the rank of N7, breaking numerous records in the process.
And thus the story begins. Shepard, highly respected, a veteran of the N7 forces, is secretly put forward as the candidate for the first human Spectre. Paired up with the Turian Spectre Sidonis, they are dropped down onto a colony that has apparently been invaded by Geth. This was supposed to be a mission to take measure of Shepard's skills.
It will become a struggle for the very survival of the galaxy.
Thoughts?
[EDIT]
I'd like to note, just for the sake of thoroughness, that while the Pre-Service History is completely canon compliant, the Psychological Profile is not. The reason is that, according to the official timeline, the events on Elysium happened before the events on Torfan. This makes it effectively impossible for Shepard to take the fall for the debacle on Torfan; while it may indeed be true that Major Kyle is very well respected, Shepard has a Star of Terra, which is the highest commendatino the Alliance can give, and it is vaguely implied that most people who have it had to die to get it, which makes the fact that Shepard survived earning one that much more impressive. There's no way the Alliance brass could hang a Star of Terra holder out to dry like that, even if they had wanted to. This setup assumes the hearing was Pre-Elysium; it doesn't work if it's Post-Elysium. So in terms of canon, this setup is not completely compliant. You do have to tweak the dates to make it work. However, it's not a major tweak, and anyone who doesn't know the timeline inside-out would never catch the problem to begin with, so I don't think it's that big of a deal.