The aim of this thesis is to identify the structure of personality below the factor level in chimpanzees, bonobos, orangutans, gorillas in terms of both facets and items and to investigate the development of these lower-order traits over the lifespan in these species. First, we aim to summarise the field of personality development in nonhuman animals at the factor level and exploring potential pathways and mechanisms that can explain how these different personality structures evolved in a wide variety of species. Next, we identify the facet structure of personality traits in four great apes using data-driven analytic methods and compare this structure amongst species. Third, we go beyond facets to the finer hierarchical level of nuances or items and explore how the greater detail available from using these levels of personality improve our understanding of how personality varies with age in the same four species. Finally, we lay out a method for the adaptation of these personality questionnaire instruments to identify personality structure in a new primate family, lemurs. These lower-order structures have great potential to increase understanding of personality in nonhuman animals and this thesis provides a solid foundation for wider adoption of these ideas.