According to GDPR, what is the definition of a 'controller'?

The definition of a 'controller' under the General Data Protection Regulation (GDPR) is indeed a person or organization that determines the purposes and means of processing personal data. This means that the controller is the entity that decides why personal data is being collected and how it will be processed. This central role involves making critical decisions about data handling practices, ensuring that such practices comply with the principles of data protection outlined in the GDPR.

The importance of this definition lies in the responsibilities placed on controllers, which include obligations such as ensuring the legality of the data processing, maintaining data security, and respecting the rights of the data subjects. Controllers are held accountable for compliance with GDPR provisions and must implement appropriate measures to protect personal data and uphold individuals' rights.

In contrast, the other options do not accurately capture the definition of a controller as per GDPR. For example, merely processing personal data does not encompass the broader role of determining the purposes and means of that processing. Similarly, a third-party entity handling data requests or a legal entity overseeing data retention policies are more specific functions that could fall under different roles within the data protection framework, such as data processors or data protection officers, rather than defining the controller's responsibilities.