The person or entity who should be primarily responsible for performing user entitlement reviews is the data owner. A user entitlement review is a process that verifies and validates the access rights and privileges of the users to the data and resources in the IT environment. A user entitlement review helps to ensure that the users have the appropriate and necessary access to perform their roles and functions, and to prevent or detect any unauthorized or inappropriate access. A data owner is the person or entity that has the authority and responsibility to define, classify, and protect the data and resources in the IT environment. A data owner helps to perform user entitlement reviews, because they help to establish and enforce the access policies and standards for the data and resources, and to approve or revoke the access requests and changes for the users. A data owner also helps to monitor and report on the access performance and compliance for the data and resources, and to identify and address any issues or gaps in the access management activities. The other options are not the primary responsible party for performing user entitlement reviews, although they may be involved in the process. IT security manager, IT personnel, and data custodian are all examples of roles or functions that can help tosupport or implement the user entitlement reviews, but they do not necessarily have the authority or responsibility to define, classify, or protect the data and resources. References = Risk and Information Systems Control Study Manual, Chapter 5, Section 5.2.1, page 5-14.