Archibald Cornwell, known to nearly everyone as Archie, is a character from the Ardley family, a wealthy and influential American clan with Scottish roots. He is the second son of the Cornwell family and the younger brother of Alistair Cornwell, as well as a cousin to Anthony Brown. Raised alongside his brother and cousin, Archie grows up under the care of his great-aunt, Elroy, after his parents are frequently absent due to travel.

Archie is often described as a cheerful and frank young man, but his most defining external trait is his meticulous attention to his personal appearance. He cultivates the image of a dandy, always dressing in the latest elegant fashions and ensuring his hair is carefully combed. This vanity extends to a strong aversion to getting dirty or ruining his fine clothes, to the point where he once admitted he would rather risk drowning than soil a silk shirt by swimming. He is generally polite, kind, and charismatic, with a natural charm that makes him quite popular. Beneath this polished surface, however, he has a more impulsive and hot-tempered side, sometimes speaking bluntly or acting recklessly, especially when he feels strongly about something. Despite his occasional vanity and impulsiveness, he possesses a deep sense of loyalty, honor, and respect for his friends and family.

Archie's primary motivation, particularly in his youth, revolves around his affection for Candice White, the protagonist. He falls in love with Candy almost immediately after meeting her, drawn to her spirited and compassionate nature, which stands in stark contrast to the more delicate and refined girls he usually prefers. However, he is also motivated by a strong sense of duty and propriety. When he realizes his cousin Anthony is also in love with Candy, and that Candy returns Anthony's feelings, Archie chooses to step aside and hide his own love, demonstrating his loyalty and respect for their relationship. Later, after Anthony's death and Candy's subsequent move to London, Archie struggles with his enduring feelings for her, even as she grows closer to another rival, Terry Granchester. His actions are often driven by a desire to protect Candy, both from her tormentors, like the Leagan siblings, and from what he perceives as the bad influence of Terry. Ultimately, his motivations shift as he matures, learning to accept unrequited love and find happiness in a relationship with Annie Brighton, who has long adored him.

In the story, Archie serves as one of Candy's key childhood friends and protectors. Alongside his brother Alistair and cousin Anthony, he forms a trio of young Ardley relatives who consistently shield Candy from the abuse of Eliza and Neil Leagan. He is a central figure in the Lakewood and London arcs, representing a potential but ultimately unrealized romantic interest for Candy. His role also establishes a direct contrast with the character of Terry Granchester. Where Archie is refined, proper, and represents aristocratic convention, Terry is rebellious and defiant of social norms, and their mutual rivalry over Candy highlights these clashing worldviews. Later in the narrative, Archie's role becomes intertwined with Annie, as his love epiphany for her leads to their eventual marriage.

Archie's key relationships are numerous and define much of his character arc. His relationship with Candy is the most significant; it is an unrequited love that persists in some form for years, though he learns to manage it for the sake of others. His bond with his cousin Anthony is one of deep camaraderie and respect, as he views Anthony as an older brother and leader, even envying how Anthony could escape punishment from Aunt Elroy with a gentle look. With his older brother Alistair, Archie shares a close and often playful relationship, looking up to him as the reliable firstborn, though he sometimes worries about his brother's eccentric inventions. His relationship with Annie Brighton begins with her long-held crush on him, but his "love epiphany" occurs when he sees her vulnerability and realizes his true feelings for her. They marry, though the novels suggest his marriage is complicated by his lingering attachment to Candy. Finally, his rivalry with Terry Granchester is intense and born of jealousy, as Archie feels that the rebellious Englishman is unworthy of Candy, leading to frequent clashes.

Archie undergoes notable development throughout the narrative. He begins as a somewhat vain and carefree youth, primarily concerned with his appearance and enjoying the company of girls. His unrequited love for Candy teaches him about sacrifice, respect, and emotional pain. The death of his cousin Anthony is a profound loss, and later, the death of his brother Alistair during World War I is an even greater tragedy. At Alistair's funeral, Archie shows significant maturity by restraining his grief and presenting a dignified front for his parents, only breaking down in private as he remembers his lost loved ones. He evolves from a jealous, impulsive boy into a man who understands duty, accepts loss, and ultimately commits to a loving marriage with Annie, even if his heart is not entirely free.

In terms of abilities and traits, Archie has no supernatural or combat-related skills. His notable abilities are largely social and practical. He is a skilled and charismatic conversationalist, adept at navigating high society. He is physically capable, being an expert swimmer, though he prefers not to demonstrate it. His greatest strength lies in his loyalty and his capacity for emotional resilience, learning to endure the pain of unrequited love and the grief of losing family members while maintaining his outward composure and sense of honor.