Which component primarily controls visual output in a computer?

The component that primarily controls visual output in a computer is the video card. This hardware is specifically designed to process and render graphics, translating data into images that are visualized on the monitor. The video card takes on the task of handling the complex calculations needed for graphics, including rendering 2D and 3D images, as well as managing video playback and gaming performance with high frame rates.

When considering the other options, the motherboard serves as the backbone of the computer, connecting all components and allowing communication between them but does not directly handle visual output. RAM (Random Access Memory) is crucial for temporary data storage during active processes and applications, impacting performance but not specifically tied to visual output. The hard drive provides long-term data storage and does not play a role in rendering graphics. Thus, the video card is the dedicated component essential for producing the images and videos seen on the monitor, making it the correct answer.