Evangeline Athanasia Katherine McDowell is a student in class 3-A at Mahora Academy who appears to be a young girl around ten years of age. This youthful appearance is a result of her true nature, as she is in fact a centuries-old vampire, having been transformed through sorcery on her tenth birthday. Despite her physical age, she is over five hundred years old, a fact she often references by referring to herself as old. Her true name is known throughout the magical world, where she has earned numerous epithets such as the Dark Evangel, the Doll Master, and the Apostle of Calamity, reflecting her formidable reputation.

Her personality is marked by a deep-seated aloofness and a cynical outlook on the world. She typically maintains an emotional distance from those around her, often speaking only to offer a critical or disparaging remark, particularly towards individuals she considers shallow or thoughtless. This cold and devilish demeanor, however, is a protective exterior that conceals a more complex inner self. Beneath her prickly surface, she possesses a softer side that she rarely shows, and she is known to genuinely enjoy quiet pursuits like the game of Go and the tea ceremony club. She is easily bored by prolonged peace and becomes frustrated with the carefree attitudes of her classmates. A notable trigger for her is being called short or little, which causes her to lose her temper quickly.

Her motivations are deeply rooted in her long and tragic history. After being turned into a vampire, she lived a life of bloodshed and developed her magical power to exact revenge on her creator. Later, she fell in love with the legendary mage Nagi Springfield, the father of her future teacher. After he rejected her advances, she tracked him to Japan. He tricked her and placed a powerful curse called Infernus Scholasticus upon her, binding her to the grounds of Mahora Academy and severely restricting her powers. He promised to free her upon her graduation but disappeared, leaving her trapped for years. This betrayal and imprisonment are the sources of her initial antagonism and her desire to be free. She carries a deep sense of guilt for her violent past, believing murder is an unforgivable sin and that her eternal life is a fitting punishment, which makes her reluctant to share her history with others.

Within the story, Evangeline initially serves as an antagonist to the young protagonist Negi Springfield. She attacks him, claiming that draining the blood of his father's son would break her curse. However, after witnessing her immense power and true abilities, Negi convinces her to become his master in magical combat. In this role, she is a demanding and harsh teacher, using a tough-love approach and expecting menial servitude from her student. She often acts as both a mentor and a gatekeeper, providing the principal cast with the training and clues they need to face greater dangers while also constantly testing their motives, will, and abilities, sometimes even aiding their potential foes to ensure they are truly worthy.

Her key relationships are central to her development. With Nagi Springfield, her history is one of love, rejection, and imprisonment, which transforms into a bitter grudge. Her relationship with his son, Negi, evolves from antagonism to a complex bond of teacher and student; she respects his intellect and tendency to ponder moral issues, and she becomes a pivotal guide in his search for his missing father. She is frequently accompanied by two partners: the doll Chachazero and the robot Chachamaru, for whom she shows genuine care. She is particularly harsh with Asuna Kagurazaka, whom she sees as someone who moralizes from a place of ignorance, yet she also reluctantly trains her when her skills prove lacking. In the sequel series UQ Holder, her story continues centuries later where she adopts the name Yukihime and becomes the leader of a group of immortals, forming a deep familial bond with Touta Konoe.

Her character develops significantly from a vengeful antagonist to a reluctant but crucial ally and teacher. She comes to accept her role as a clarifier for others, showing them the difficult decisions before them and allowing them to choose their own path, even if she insists she does so out of boredom or for her own ends rather than benevolence. She boasts that her most important success as a teacher was guiding Negi through a morally gray conflict, making him understand that truly significant actions always come with costs to others.

Evangeline possesses a vast and terrifying array of notable abilities. As a Shinso, or True Blood vampire, she has Class A immortality, granting her eternal youth, immense regenerative abilities, and enhanced physical attributes like strength and speed. She has overcome most traditional vampire weaknesses, including sunlight, becoming a High Daylight Walker. She is a master of dark magic and specializes in powerful ice-based spells, capable of defeating god-like adversaries with ease. Her renowned title of Doll Master comes from her ability to animate dolls and control people like puppets. She is also the creator of the forbidden dark magic technique Magia Erebea, which fuses spells with the user's soul. Even when stripped of her magic, she remains an extraordinarily skilled fighter, having mastered the Japanese martial art of Aikido, which she claims to have learned from its founder during her travels in Japan.