Which aircraft control surface primarily affects a pilot's roll movements?

The ailerons are the primary control surfaces used to affect a pilot's roll movements. Located on the outer portions of the wings, ailerons operate in opposition to one another. When one aileron is deflected upward, the opposite aileron is deflected downward. This creates a differential lift on the wings, causing the aircraft to roll towards the wing with the downward-deflected aileron and consequently achieve a turn.

While the rudder is essential for controlling yaw, it does not influence the roll directly. Elevators are primarily responsible for controlling the pitch of the aircraft, allowing the pilot to ascend or descend. Flaps are designed to increase lift during takeoff and landing but do not directly contribute to rolling the aircraft. Therefore, ailerons are the specific control surface that directly facilitates roll movements, making them the correct answer.