What is the definition of Controller according to GDPR?

Article 4 dealing with the GDPR Definitions says in its paragraph 7:

‘controller’ means the natural or legal person, public authority, agency or other body which, alone or

jointly with others, determines the purposes and means of the processing of personal data; where

the purposes and means of such processing are determined by Union or Member State law, the

controller or the specific criteria for its nomination may be provided for by Union or Member State

law.