Abbas Sofian, born in 1166, had a rather rough childhood. His father - captured by the Saracens in 1176 and tortured to the breaking point - vanished from his son's life when Abbas was still a boy. Assuming he had been abandoned, Abbas fell into a deep depression, which only his friendships and devotion to his Mentor, Al Mualim, could ease.
But all this changed a few years later when his friend and confident, Altaïr, passed on what Abbas assumed was the cruelest of lies: that Abbas's father had betrayed the Assassin Order while under interrogation, and had later killed himself to escape his shame. Infuriated, Abbas refused to believe this hard, unvarnished truth - a truth Al Mualim refused to corroborate or deny. So from that point forward Abbas regarded Altaïr as a liar and a deceiver- a man too devious and reckless to follow the Creed's most austere tenets.
As he grew into adulthood, Abbas matured into a skilled and respected Assassin, but his personality always left something to be desired. Humorless, with an almost fetishistic passion for the Brotherhood, he loathed both Al Mualim's favoritism, as well as Altaïr's loose interpretation of the Creed. But he remained a loyal servant for many years, always hiding his gnashing contempt for his former friend.
Staying silent was difficult, however, and over the course of Altaïr's precipitous rise to the rank of Master, and later Mentor, Abbas found himself filled with a crippling hatred he could barely contain. It was only a matter of time before he burst.