Who holds resonponsibility for data security?

Data Custodian

One of the data protection positions.  A Data Custodian is often a person in an IT position who oversees infrastructure management for storage and security. Data Custodians concentrate on the "how" of data storage, and likely get day-to-day tasks from the Data Owner. They can structure or restructure a relational database system, employ middleware to support a central data warehouse, or provide workflows or schemes that demonstrate how databases are organized.