A Google Analytics API developer integrates Google Analytics data with other applications. They use Google's API (Application Programming Interface) to request, collect, and manipulate data for customized reports, analyses, or to enhance website functionality. This could include tracking user behavior, engagement, conversion rates, or other metrics. They may also create custom dashboards or applications to display this data in a more accessible or meaningful way. Their work enables businesses to make data-driven decisions, optimize their website, and improve their marketing strategies based on real-time and historical data.