Hathaway was the successor of Isabelle Ardant, who had been impressed by him and made mention of the historian a number of times in her files which brought him to the attention of Alan Rikkin. Upon taking his position in the Inner Sanctum, Hathaway gave a presentation to its other eight members in which he put forward his belief that the Animus was not being used to its full potential in their search for Pieces of Eden and Assassins. Seeing the methods such as those by Abstergo Entertainment–which utilized people largely ignorant of the significance of what they witnessed in the past–as more data gathering rather than application of knowledge, Hathaway argued that greater work could be done in less time by sending a Templar like himself into the past who could appreciate the greater context of what they saw and therefore discover clues that others simply didn't know to look out for.
To that end, he put forth a theory that the Sword of Eden which had become damaged as it was passed down through history from Grand Masters Jacques de Molay and François-Thomas Germain to the Assassin Arno Dorian and eventually into the office of Alan Rikkin himself was the very same weapon wielded by Jeanne d'Arc during the Hundred Years' War. It was Hathaway's belief that by exploring the memories of his ancestor Gabriel Laxart, who fought besides Jeanne d'Arc, he would be able to observe the sword's abilities firsthand and thereby have the opportunity to reactivate them in the present day.
Rikkin gave Hathaway a deliberately tight one-week schedule to test this new direction that the professor wanted the Historical Research Division to take and assigned Victoria Bibeau to assist him, a move which immediately reduced the timeline to six days as Bibeau needed to fly in to London from The Aerie.
- While not clearly confirmed, Assassin's Creed: Heresy hint that Simon is a descendant of Jeanne d'Arc, as after her faked execution the maid shared her life with Simon's known ancestor, Gabriel Laxart, who fathered children during that time.
- Hathaway is in couple with hacker and fellow Templar, Anaya Chodary.