The thesis examines the processes as they occur in the actor ́s mind during work on the character while rehearsing and acting. It also describes extensively the steps prior to the rehearsal process and acting from the actor ́s point of view regarding the actor ́s mental states. Additionally, the focus is on various approaches to character building during rehearsals and on various wals of working with the text. In her analyses, the authoress is aware of the specific differences of the theatrical genres. The thesis is based largely on her experience.