Katia Tien was born to Altus and Naya Tien in Northshire during the First War (1), while her father was away fighting the Orcish Horde. Her mother, Naya, and older brother Nikolas lived by the Abbey in Northshire for the duration of the war. Katia saw her father for the first time when he returned to Northshire to collect his family and flee to the north: the Orcs had turned the armies of Stormwind and were even at that moment marching on the Keep (4). Despite the turbulent circumstances, Katia took a quick and particular liking to her father and his gentle nature.
The Tiens sailed north to Southshore, with the refugees of Stormwind. Katia was only four when her family was banished from Alterac by her grandfather, Caiberd Layette, and when she was five said goodbye to her father as he marched to war for the second time. During the Second War (6), she helped her mother as she made bandages to send to the front lines.
After the Horde's defeat (7), Altus took his family to live in the Hinterlands, near his dwarf friend Dobrin Wildhammer, with whom Altus had been friends for years. With her brother, Katia learned much from her parents, from daily chores and tasks to basic education like reading, writing, and other subjects. The children were also instructed by their father in the ways of the Light, in the teachings of which Katia developed a particular interest. Naya taught her children about magic and the arcane arts, but Katia paid less attention to this (conversely, Katia's brother Nikolas showed more interest in his mother's magic instruction than learning about the Light).
When Katia turned 17, she left for the Monastery in the northern Tirisfal Glades to study the Light and become a priestess (18). She was well accepted by the clerics and priests at the Monastery, in part because she displayed great talent for using the Light's power. Katia eventually became a respected student to Sally Whitemane, one of the Monastery's most highly-ranked priestesses.
Katia was relatively sheltered from the Third War and the Scourge Invasion of Lordaeron (25). While better-trained and more seasoned priests, clerics and paladins went to aid the Alliance, Katia and many others stayed behind to continue training, largely in preparation should the Monastery come under seige. The actual war with the Scourge was short, as much of the Undead went to and were defeated on the far continent of Kalimdor. But sizable Scourge forces had been left behind in Lordaeron, and fighting continued. Though initially offered a chance to flee south to escape the fighting, Katia and many others chose instead to stay, believing it to be their responsibility to defend the Light against the dark and demonic armies of the Scourge.
As what remained of Lordaeron's forces battled the Undead, a faction was born from the zeal and fervor with which some of the Alliance soldiers fought. The Scarlet Crusade began in honor and nobility, as a force dedicated to the reclamation of all that the Scourge had taken. But many of the Crusade's leaders and soldiers soon became obsessed with their goals, to the point of fanaticism. Spurred on by an increasingly-paranoid leadership, the Scarlet Crusaders began to use extreme and radical methods to both fight the Undead and to protect themselves from infiltration by the Undead. Two events, in particular, helped to solidify the Crusade's identity as an extremist and fanatical faction. First, in the city of Hearthglen, a high ranking spiritual leader of the Crusade claimed the Scourge had tried to assassinate him. Grand Inquisitor Isillien told the people the Scourge had turned his servant into an Undead spy, despite the fact the servant still looked human. Isillien claimed, and convinced many, that the Scourge had somehow developed that ability to disguise their spies as the living, and were therefore much harder to detect. His claims led the Crusade to adopt many practices that were unethical, cruel and evil, though they were seen by the Crusade as necessary to protect itself from infiltration.
The second catalyst for the Crusade's proverbial fall from grace was the death of one of the Crusade's founders, Highlord Alexandros Mograine, at the treacherous hands of his own son Renault. Mograine's death left the Crusade in the hands of those who had been consumed by madness: Renault, Isillien, and others.
Renault Mograine was assigned to command the Crusade's forces at the Monastery. Though she didn't really like him, Katia felt that duty required her obedience to him. When Alexandros Mograine's trusted friend, High Inquisitor Fairbanks, came to the Monastery proclaiming Renault's treachery, some believed him and left (these would later be the founders of the Argent Dawn, a faction who also sought the defeat of the Undead but by more just and sane methods). A small part of Katia wanted to believe that Renault was capable of such treachery, but her trusted teacher Sally, now called High Inquisitor Whitemane, convinced her that Renault was true to the Crusade's cause, and was indeed the right man to take his father's place.
Katia remains to this day (29) at the Monastery, occasionally venturing out to assist the Crusade in keeping back the Undead forces, who took over and set up base in the Tirisfal Glades just south of the Monastery. Her mother and brother know where she is and where her allegiance lies, but while Naya remains quietly supportive of her daughter, Nikolas has made no attempt to hide his disdain for the Crusade. Katia has recieved several letters from him, asking her to look closely at what the Crusade does to both living and Undead, but his pleas have fallen on quiet ears. Fueled by anger at her father's death by the Scourge, and spurred on by the subtle whisperings of her mentor, High Inquisitor Whitemane, Katia is devoted to the Crusade and to the eradication of both the Undead and those who would oppose the Crusade.