Who is the primary advisor to the President on matters of national security?

The National Security Advisor serves as the primary advisor to the President on matters of national security. This position is crucial because the National Security Advisor coordinates security policies and responses and is responsible for informing the President about key international issues and crises. Unlike other advisors, this role is specifically focused on the intricacies and complexities of national security matters, including defense, foreign policy, and emergency responses.

While the Secretary of Defense oversees the Department of Defense and manages military operations, and the Director of National Intelligence focuses on the intelligence community and assessing threats, neither of these roles directly advises the President on a wide range of national security issues as comprehensively as the National Security Advisor. The Chief of Staff plays a vital role in managing the President's schedule and ensuring effective communication within the White House and does not hold the same focused responsibility for national security matters. Thus, the National Security Advisor's prominence in providing strategic counsel makes this answer the most accurate choice.