Olga was a Great Light Enchantress, and is an old friend and occasional lover of Geser. She is very old for an Other, dating back to the founding of the Treaty, but was made into an Other at an early age, as she only appears to be in her twenties. Geser has a number of pet names for her (Olya, Olyushka, etc.) Whenever he refers to someone whose name begins with “Ol”, he is likely referring to Olga.
Olga has been around for a long, long time; she’s been around since before the Treaty was formed. Decades later, she was arrested and tried by the Inquisition, stripped of her powers and rank as a Great Enchantress, and imprisoned in the shape of an owl for breaking obligations she had to the Light. In Night Watch, she states that her predicament came about because of a deal made with the Darkness. However, she is allowed to return to human form during wartime for half an hour every day with access to menial Light powers, because she is very experienced as a warrior and in dealing with Inferno breaches. During World War II, she protected Hitler and Stalin from Dark Vortices and also gave birth to Timur Borisovich, fathered by Geser.
Olga becomes a main character of Night Watch very quickly as most of story one, “Destiny”, is part of Geser’s plan to get her reinstated to Great Other status. She is paired with novice Light Magician Anton Gorodetsky after two vampires try to illegally blood a human boy named Yegor and Anton discovers Svetlana Nazarova, a woman cursed by a Dark Vortex and a future Great Enchantress. The pair destroy the Dark Vortex and save Yegor from the remaining vampiress, turning Yegor into a Dark One in the process. In stories two and three of the book, Olga takes more of a backseat role. In story two, "Among His Own Kind", Olga has been officially reinstated to her human form by the Inquisition, but still lacks her magical capabilities. During the course of the story she spends most of her time in Anton's body, as Geser performs a body switch to shield Anton from accusations of murder of Dark Ones made from the head of the Daywatch, a Great Dark Magician named Zabulon. In story three, "All for My Own Kind", she sleeps with Ignat at a party at Tiger Cub's house and later reveals to Anton that Svetlana is intended to to use the Chalk of Fate to rewrite Yegor's Book of Destiny. In the meantime, Olga also uses the Chalk to edit Svetlana's Book of Fate, making her future daughter destined to be born sooner.
Olga is virtually nonexistant in Day Watch, only appearing briefly at the Tribunal in Moscow at the end of A Stranger Among Others, and at the Tribunal in Prague at the end of Another Power.
Olga is barely featured in Twilight Watch, only appearing at the train station when hunting for the Fuaran. She is later one of the Others who gives Power to Anton when he attempts to stop the High Vampire Kostya Saushkin.
During the events of Last Watch, Olga is busy managing the businesses of the Nightwatch. In the last of the three stories, "A Common Destiny", she leaves the Nightwatch headquarters with Anton to search the home of vampire Gennadiy Saushkin, who is under suspicion of being the second member of a mysterious trio known as The Last Watch. She discovers the fifty drained human corpses hidden in Gennadiy's home, confirming the suspicions.