Characters are a crucial element in any piece of fiction, but how are they created in a historical novel? This two-part thesis explores the question from both creative and theoretical perspectives. The creative component is a historical novel, ‘My name is John Tyndall’, based on the life of the eponymous Irish scientist. It includes some of Tyndall’s major achievements, such as formulating the physical basis of the greenhouse effect, and giving the first explanation for the colour of the sky, but it also incorporates significant fictional innovations. In my fiction, the man known to history as John Tyndall is in fact a brilliant imposter. The story follows an unnamed protagonist, a gifted, impoverished young autodidact with scientific aspirations, who becomes acquainted with wealthy, mediocre student John Tyndall. When Tyndall dies in an accident, our protagonist seizes the opportunity to assume Tyndall’s identity and goes on to become the pioneer physicist we know today. Structurally, the novel begins with an invented protagonist living an entirely fictional life. After Tyndall dies, it gradually shifts towards the factual historical record. By the end, the narrative conforms with this record except for the conceit framing the novel. This shift from pure fiction to maximally faithful historical fiction is the key challenge in terms of creative practice, and how to create a character that enables it is the central question underpinning my research. The critical component is a dissertation analysing the relationship between historical figures and their fictional representations. It focuses on the Cromwell trilogy (Wolf Hall, Bring Up the Bodies and The Mirror & the Light) by Hilary Mantel, a widely acclaimed historical fiction writer, known for her rigorous research. This thesis constitutes a dual examination of the process of characterisation in historical fiction, and it contributes to our understanding of this elusive subject.