Abstract: In this paper, we present an approach based on the principle that psychological capacities, especially personality traits, influence the decision making process of rational agents. Using a three-level (trait, facet, scheme) extension of the FFM/NEO PI-R taxonomy facilitating its computational implementation, we propose a model for the expression of personality traits in terms of so-called influence operators that add meta control rules to the cycle of rational BDI agents. We distinguish eight different classes of influence operators, depending on the step of the deliberation cycle that they influence and on the operand to which they are applied (goals, actions, plans or functions). Concrete examples are provided through a complete definition of the operators necessary to express one of the personality traits of the Five Factor Model, Conscientiousness, resulting in a set of 30 operators. Finally, we discuss the way to design a specific character through the use of an activation matrix, providing values for each scheme and operator.