The purpose of this study was to develop an understanding of the interaction between expertise, managerial role, and subjective behavioural characteristics. The research seeks answers to the question: What shapes the managerial decision-making processes of an expert? Four case studies examined the decision-making processes of four domain experts who have taken on managerial roles. The studies follow a triangulated approach using interviews, observations and psychological evaluations to discover the dominant decision making processes of the experts in their managerial roles. This study includes interviews with each of the four experts, interviews with people associated with them in their work environment, the researcher’s observations, and three psychological evaluations. The research indicates that the subjective characteristics of the experts studied may determine the domain in which they became expert, and consequently the managerial role that they chose and also the managerial decision-making processes that they follow. The experts’ decision-making processes seem to be shaped initially by their subjective characteristics, second by their expertise and last by their managerial role. There was however, an indication that these experts dichotomise their managerial decision-making processes to distinguish between decisions that directly involve people and other decisions. Managerial requirements create situations that require the use of the experts’ subjective characteristics that are not otherwise used. It is therefore concluded that the subjective characteristics of the experts studied have shaped their managerial decision-making processes. The outcome from a study of four experts is not expected to be valid for all experts, however it may add weight to an argument that more consideration needs to be made of the two-way interaction between expert and domain.