UML class diagrams can be used as a language for expressing a conceptual model of a domain. In a series of papers [1,2,3] we have been using the General Ontological Language (GOL) and its underlying upper level ontology, proposed in [4,5], to evaluate the ontological correctness of a conceptual UML class model and to develop guidelines for how the constructs of the UML should be used in conceptual modeling. In this paper, we focus on the UML metaconcepts of classes and objects from an ontological point of view. We use a philosophically and psychologically well-founded theory of classifiers to propose a UML profile for Ontology Representation and Conceptual Modeling. Moreover, we propose a design pattern based on this profile to target a recurrent problem in role modeling discussed in the literature. Finally, we demonstrate the relevance of the tools proposed by applying them to solve recurrent problems in the practice of conceptual modeling.