The primary role of a software tester is to ensure that software applications meet specified requirements and function correctly before release. They design and execute various test cases, identify bugs, and verify that fixes work effectively. Testers play a crucial role in enhancing quality assurance by assessing the software's performance, usability, and compatibility across devices. Their feedback helps developers make informed improvements and minimizes the risk of defects that could impact user experience or lead to significant financial losses for the company.