A Google Website Optimizer developer uses Google's optimization tools to improve website performance. They conduct A/B testing, multivariate testing, and analyze user behavior to increase engagement, conversions, and user satisfaction. They identify areas of a website that need improvement and design changes to enhance user experience. They use analytics to track the success of these changes, utilizing data to make informed decisions about further modifications. They also work on improving site speed, mobile optimization, and SEO. The ultimate goal of a Google Website Optimizer developer is to create a website that meets the needs of users while achieving business objectives.