An entity such as any organization, person, or body that determines the purposes, conditions, and means of processing personal data of data subjects; controls the data; and is responsible for it, alone or jointly.
Examples of individuals as data controllers are general practitioners, pharmacists, and politicians. These individuals keep personal information about their patients, clients, constituents, and so on.
Examples of organizations as data controllers, are organizations which are private or government-owned, large or small, for profit or not for profit, that keep personal information about their employees, customers, and so on.