Wilhelm has white hair and blue eyes. He wears a white shirt, white vest, black bowtie, black dress pants, and a black and blue coat. Due to his daily training, he is still muscular at his old age and his back is perfectly straight. When he was young, Wilhelm had brown hair and wore the Royal Guard uniform.
Wilhelm is a refined man with a highly gentle and humble demeanor. However, underneath that even temperament is a fierce warrior who often is the first to help when something happens. This wasn't always the case, as in his youth, Wilhelm was the very opposite of who he was in his later years.: brash, afoot, short tempered, lonely, and often cold with others. He was a troubled individual who devoted himself wholly to the sword and cared for little else. Even so, he knew how to analyze a situation, always finding a way out. Nonetheless, Theresia greatly influenced his personality, which caused him to become increasingly sociable and protective, achieving more results during the Demi-human War. It was through her most of all that he would become the person he is today.
Wilhelm was born the third son of the Trias family, who lived in the countryside of the Kingdom of Lugnica. They were an old house of nobility situated in one of the kingdom’s most remote northern province, which bordered Holy Kingdom of Gusteko, and had the responsibly for managing the some of the territories there. Once a proud warrior family, their days of military glory were a thing of the past, and by the time Wilhelm was born, they were little more than a small barony running meager lands with a small population of serfs. Unlike his much older siblings, Wilhelm had neither the claim to inherent leadership in the family nor the knack for civil governance, leaving him little hope in his own future prospects until the day he picked up his family's treasured sword. Enchanted by the blade, he would spend 6 years of his youth in the mountains near his home swinging it day and night as it gave him a sense of peace and purpose that his life had lacked up til then and each time he swung it, he felt himself growing stronger. By the time he was 14, he had become the most skilled swordsman in the domain. However, one night, due to a severe quarrel with his eldest brother over his future, he left his family and traveled to the royal capital to become a knight.
At the time, the country had been going through a civil war with the Demi-human Alliance, a group of demi-human tribes, for some years that began in its eastern region when Wilhelm enlisted. From the time of his first battle, Wilhelm would stand out and make a name for himself due to his near unparalleled skill despite his age. On the field, he was a ferocious and tenacious soldier who leaped into enemy formations, leaving nothing but scores of corpses as he cut through with reckless abandon and a wicked smile on his face. His daredevil like behavior and action earned him the moniker "Sword Demon" from the royal military forces and foe alike who looked at him in awe, fear, and hatred. However, despite his military achievements and national renown skill, Wilhelm received no promotion. This was partly because he refused, but also since Wilhelm was very anti-social, barely having anyone he called friends, rarely conversing with anyone, and fighting regardless of the danger it brought his allies. Knighthood, which rested on things beyond battle like bonds between people, seemed ill-fitting for him as someone who only fought to suppress the discontent in his heart.
For 3 years, Wilhelm continued to live his life on the battlefield like this until one day, due to the changing conditions of the civil war, he found himself on forced leave in the royal capital for a time. It was during this period that a dissatisfied Wilhelm with too much time on his hands and little to do with it met Theresia in an abandoned construction site within the royal capital where he had come to train regularly. This meeting, although beginning innocuously at first, would eventually change Wilhelm's life in a profound way. Despite his best efforts to remain detached from her company in over 3 months, he found himself increasingly drawn to Theresia, who often rebuffed his crude manners and afoot persona. Unaware of the subtle changes in his heart at first, subconsciously he started looking forward to their ritualistic meetings, which eventually led him to question the real reason why he had continued to walk the path of the sword while he had been avoiding his life up until now. Coming to an epiphany, Wilhelm realized that he had been using it as an excuse to run away from his problems at home. Wanting to do something his older brothers couldn't and support his family in his own way as they did. Accepting this fact, Wilhelm found himself caring about things he hadn't in a long time, becoming less and less concerned with taking the heads of his enemies over prioritizing the safety of his comrades. For such an infamous figure in the royal military, his changes did not go unnoticed and was mostly welcomed among his peers. Wilhelm received calls and support for knighthood once again, but this time, he took it up because he found a new reason to wield his sword, no longer just for his self-satisfaction, but rather to protect the things he cared about and the happiness of one person who became irreplaceable in his life.
Unfortunately, disaster struck shortly after Wilhelm attained his wish when news of the intensifying civil war had spread all the way to far reaches of the northernmost regions of the country where the Trias territory lay. Defying conduct, Wilhelm immediately raced home, only to find his hometown already sacked and faced with more demi-humans forces than he ever fought before. Wilhelm, who seemed to finally be hitting the limits of his ability, would have nearly perished as a result had he not been saved by the newest incarnation of the Sword Saint, who turned out to be none other than Theresia. Feeling humiliated, but captivated by her display of swordsmanship that he could never reach, and most of all indignation at war, society, and his weak self that had forced her to resign herself to the inescapable fate to take up the mantle of "Sword Saint", Wilhelm confronted Theresia, leading them to part ways with their resolve to protect the other. 2 years would pass before they saw each other again at the ceremony to celebrate the end of a decade long war. There, a much stronger Wilhelm entered an impassioned duel with Theresia in which after a close match, the former defeated the latter. Making good on his promise, Wilhelm freed her from the duties and burden of Sword Saint and took them up in her stead so that she could live the life she wanted. A year later, they would go on to marry one another.
In the present story, Wilhelm has come under the service of Crusch Karsten after leaving the Royal Guard and the House of Astrea nearly 14 years ago to gain her assistance in hunting the White Whale in exchange for his support for her in the Royal Selection.
Master Swordsman: Although self-taught, Wilhelm is highly skilled with the sword and honed his extraordinary talent for swordsmanship to superhuman levels to where he was able to barely defeat the previous Sword Saint in a duel. He was also considered to be a threat to the Demi-Humans during the Demi-Human War due to his menacing appearance and unparalleled skill that earned him the alias of Sword Demon (剣鬼 Kenki).
- According to the author, Wilhelm's birthday is May 7.
- Wilhelm was originally meant to be a simple coach driver however, in the "reader feedback" column at Shousetsuka ni Narou website, a reader left a comment asking for explanation of Wilhelm's character. Tappei then decided to greatly elaborate on his character.
- Wilhelm looks similar to Valkenhayn R. Hellsing from BlazBlue.
- Aside from being her servant, Wilhelm acts as Crusch's sword instructor.
- Out of all the swordsmen Wilhelm encountered, Veltol Astrea is the one he respected the most, despite the latter being below average with the sword.
- If Theresia and Wilhelm never met, he would have died some time during the Demi-Human war.