Formerly a member of the Assassin Brotherhood, Shay devoted his Templar career to hunting down his old associates. Aboard his ship, the Morrigan, Shay's travels brought him to New York and the Appalachian Mountains, among other locations.
Shay Cormac was born sometime around 1731 in New York City, to a family of Irish immigrants. Living in a rougher part of the city, Shay had a knach for getting himself into trouble, and was constantly protected by his closest friend, Liam O'Brien. When he grew older, Shay enlisted in the British Army, but left sometime after his father died at sea in 1748.
Shattered and desolate, Shay was helped once again by Liam, who managed to get his friend back on his feet. Later that year, Liam introduced Shay to his Mentor, Achilles Davenport, and Shay joined the Brotherhood not long after. Over the next four years, Shay devoted himself to the Colonial Assassins, serving dutifully. However, he still pondered the ambiguous areas between the motives of the Assassins and those of the Templars, their sworn enemies.
In 1752, while on a mission in the North Atlantic, Shay and Liam met with their comrade, Louis-Joseph Gaultier, Chevalier de la Vérendrye, who was supposed to meet with smugglers carrying valuable cargo. When the smugglers were intercepted and captured by the British, Shay infiltrated the smugglers' camp, eliminated the British guards, and commandeered the ship the soldiers had come on, a sloop-of-war named the Morrigan.
- "Life's hardest choices are the ones that force you to question your own moral code."
- ―Shay, regarding his ties to both the Assassins and the Templars.
In his youth, Shay was a cocky, arrogant, and talker man who didn't take his role as an assassin seriously, a trait that made him rather unpopular with some of his assassin partners, specially with Louis-Joseph Gaultier. Nonetheless he deply cared for his allies and was devoted to the assassin cause; hoowever, this didn't stop him from complaining about some of the assassin's actions and morals, even questioning if they were really different from the templars, their archenemies. Cormac had a sense of honor and standards that led him to distrust the creed and eventually abandon them; particularly, he was disgusted to find that his assassin objectives, the templars he had to kill, Lawrence Washington, brother of George Washington, was an already terminal patient of tuberculosis. Shay was also notably for his grudge against killing innocents, and kept his sword away of innocent people even after joining to the templar creed.
After the disaster on Lisboa, Shay lost all faith and trust on his friends and the assassins, his personality and beliefs, making him doubt of many things, initially distrustful on the templars, Shay found new allies and a creed whose beliefs were more on par with what he believed was the right thing; however, Shay never was able to see the real goals of the templars, whom were merely manipulating him in order to drive him to their cause and vision of the world.
Despite feeling betrayed and swearing vengeance against the assassins, Shay showed some signs of regret and pain at killing some of his most close ex-friends and loved ones. like his love interest and teacher Hope or his ex-best friend Liam, who Shay honored in his demise by wearing him with his hood (is implied that Liam did in fact give the manuscript to Shay seconds before dying). Shay also was aware of his own darkness and bad actions, as when Adewale calls him a monster on his last moments, Shay agree with him in that statement, however, he kept his belief and was willingly to do anything to make what he considered right.
Shay was noticeable for being very independent, and firmly disapproves when anybody mentions he has luck, claiming "i make my own luck" any time anybody says he had luck.
Over time, Cormac developed himself into a cold, ruthless and manipulator templar, leaving most of his redeeming qualities in the past, however, he still had a sense of honor and some standards, as he convinced Haytham Kenway to spare Achillies' life to show the world still has some sort of humanity, as well refusing to kill innocent lives (he only kills civilians on gameplay territory, which is considered non-canon acts outside history campaign). Despite his grudge against amoral acts as massacre and murder of innocent, Shay never betrayed or mistrusted the tamplar creed for its terrible and amoral acts such as war and revolution, showing that in the end, he was completely consumed by templar cause and noting else, abandoning all his morals and standards and becoming a true coldblood templar.