Data (pirate ship) is a valuable asset in (pirate) organizations. Data Owners (captains) are usually senior managers in the organization that are accountable for data and have the authority to make decisions about data. They appoint Data Stewards (deckhands) to do all the work.
Data Stewards usually understand data much better. Their role is to test quality, fix data, document it, write definitions, policies and rules. Data Stewards is a role, and does not have to be job title.