Isobel Callaghan
The protagonist of the novel, Isobel is a thoughtful, yet spirited young woman who is defined by her devotion to literature. I for Isobel is delivered entirely from her perspective. At first, she is depicted as a young girl; at this stage, Isobel's main concerns in life are her schoolwork, her Catholic upbringing, and the remarkably vicious parenting style of her own mother. After her mother's death, the young adult Isobel finds employment in an import office, attends Business College, and tries to settle in at Mrs Bowers' boarding house. However, Isobel's literary interests do not wane, and lead her first to a group of budding poets and literary scholars of roughly her own age—then to the independent commitment to writing that she embraces at the end of the novel.
Isobel's Mother (May)
Other than Isobel herself, Isobel's mother is in many ways the strongest presence in the opening stages of Witting's novel. (Her death under ambiguous circumstances keeps her from playing a role in the novel's later chapters, which depict Isobel's adulthood.) As a parent, she can be breathtakingly cruel. May consistently accuses her younger daughter of dishonesty and selfishness; on a few occasions, she also lashes out and physically attacks Isobel and Isobel's possessions. However, May is an insecure woman and is not simply regarded by Isobel as an unpleasant character: from Isobel's father to Isobel's neighbor Mrs Adams, characters other than the beleaguered young Isobel view May in a negative light.
Isobel's Father (Rob)
An unassuming man who is depicted mostly through Isobel's memories and through the conversations of people who knew him, Rob's presence (or absence) creates a few narrative tensions: at one point, exasperated by his spouse's nagging, he attacked Isobel's mother with a knife. Rob's death by illness has also worsened the relationship between his two adult sisters, Aunt Yvonne and Aunt Noelene, and Isobel's mother.
Margaret
Margaret is Isobel's older sister. Like Isobel herself, Margaret is mostly a studious and well-behaved girl, although she does not share Isobel's passion for literature in any clear way. At least on the basis of the events depicted in I for Isobel, Margaret also receives kinder (or at least less violent) treatment from her mother, Mrs Callaghan.
Caroline
Caroline is a girl and Isobel's companion during Isobel's stay at Mrs Terry's lakeside boarding house.
Mr Mansell
Mr Mansell is a man on vacation at the lakeside boarding house. He gives Isobel a birthday present in the novel's first section.
Auntie Ann
Auntie Ann is Isobel's great-aunt, who the young Isobel visits and who treats Isobel with leisurely kindness.
Aunt Noelene
One of the sisters of Isobel's father, Aunt Noelene manages a dress factory and brings the young Margaret and Isobel clothes and money. After the death of Isobel's mother, Aunt Noelene serves as something of a guardian for Isobel, making her the present of a coat and advising her on how to get ahead in the workplace.
Aunt Yvonne
The other sister of Isobel's father, Aunt Yvonne is married and lives in the countryside; she looks after Margaret after the death of Isobel's mother, though she is a less prominent figure in the narrative than Aunt Noelene.
Mrs Bowers
Mrs Bowers is the detail-oriented and somewhat judgmental woman in charge of the boarding house where the young adult Isobel stays for a time. Though initially accepting of Isobel, Mrs Bowers becomes increasingly hostile and disapproving.
Mrs Prendergast
Mrs Prendergast is a woman who often keeps Mrs Bowers company, and is especially preoccupied with the subject of death.
Madge
Mrs Bowers' adult daughter, Madge apparently observes Buddhist devotions; she also marries a young man named Arthur who shares the same religious leanings. The marriage is a source of tension between Mrs Bowers and Madge, who leaves her mother's boarding house to live with her new husband.
Betty
One of the boarders at Mrs Bowers' house, Betty is significantly older than Isobel, but is attractive, independent, and even somewhat scandalous in her lifestyle.
Mr Watkin
A reserved and self-assured older man who boards at Mrs Bowers's house, Mr Watkin is on good terms with his fellow residents and is a proficient card-player.
Tim and Norman
They are two lively younger men who board at Mrs Bowers'.
Mr Walter
Mr Walter is the head of Lingard Brothers Importers; he brings Isobel on in order to translate the company's German mail.
Mr Richard
The bother of Mr Walter, he watches Isobel as she works (and thus proves a source of discomfort and irritation for Isobel).
Olive, Rita, and Nell
Olive, Rita, and Nell are three young women who, with Isobel, are employed at Lingard Brothers Importers. Isobel is on good terms with these co-workers, but does not form close or enduring friendships with them.
Frank
Frank handles the inventory at Lingard Brothers Importers and often has an honest, amiable relationship with Isobel. Despite his steady employment in a modern business, Frank is politically committed to Communism; he is obliged, however, to keep his political views to himself.
The "Special Crowd"
The "special crowd" is a group of young poets, intellectuals, and literature students central to "Glassware and Other Breakable Items," the novel's longest section. The "special crowd" consists of several different characters: Mitch, Nick, Trevor, Kenneth, Janet, Vinnie, and Helen. Some of these characters have individually minor roles, but together they represent a community that Isobel finds at least temporarily welcoming.
Nick
A member of the literary group, Nick stands out in Witting's narrative for two reasons: he is Diana's love interest, and he dies (suddenly and surprisingly) when he is hit by a car.
Trevor
Trevor is a member of the "special group" who tries (unsuccessfully) to form a romantic attachment to Isobel.
Diana
The dark, imposing, and obsessive young woman who was once in a relationship with Nick, she continues to brood over Nick while he is alive, but reacts with apparent nonchalance to Nick's death.
Mrs Drummond
Mrs Drummond is Nick's mother. She reacts first with composure and then with vocal distress to her son's death.
Kate
Kate is a woman (mentioned but unseen) who criticizes Isobel in the novel's final section.
Michael
Michael is a young man who has a one-night stand with Isobel. Isobel steals a book from him.
Mrs Adams
Mrs Adams is a woman from the neighborhood where Isobel grew up. During her girlhood, Isobel had written a poem about Mrs Adams's cat, Smoke; Mrs Adams was fond of the poem and tells Isobel as much when the adult Isobel reappears.
