A Manual Testing Developer performs tests on software manually to identify any bugs or issues. They create test cases, validate that features work as expected, and document their findings to improve software quality. On the other hand, an Automation Testing Developer writes scripts and uses automation tools to execute tests. They design, develop, and maintain automated test scripts, ensuring the software works efficiently and as intended. Automation testing increases speed and accuracy of testing, allowing frequent repetitions. Both roles aim to deliver high-quality, defect-free software, but use different methodologies; manual for exploratory and ad-hoc testing, automation for regression and large data set testing.