Roles are meant to capture dynamic and temporal aspects of real-world objects. The role concept has been used with many semantic meanings: dynamic class, aspect, perspective, interface or mode. This paper identifies common semantics of different role models found in the literature. Moreover, it presents a conceptual modelling pattern for the role concept that includes both the static and dynamic aspects of roles. A conceptual modelling pattern is aimed at representing a specific structure of knowledge that appears in different domains. In particular, we adapt the pattern to the UML. The use of this pattern eases the definition of roles in conceptual schemas. In addition, we describe the design of schemas defined using our pattern in order to implement them in any object-oriented language. We also discuss the advantages of our approach over previous ones.