A MediaWiki developer designs, develops, and maintains MediaWiki software - a free and open-source wiki package written in PHP. They work on the core application and its extensions, ensuring optimal performance, functionality, and user-friendliness. They are also responsible for troubleshooting and resolving any technical issues. Developers often collaborate with other team members, including system administrators and designers, to improve and update the software. They also contribute to the MediaWiki community by sharing their code, participating in discussions, and assisting other developers. Their goal is to create a robust and efficient platform for creating and managing wiki-based websites.