A ClustalW developer is responsible for designing, implementing, and maintaining the ClustalW software, a widely-used tool for multiple sequence alignment of proteins and nucleotides. They ensure the software can effectively compare and analyze biological sequences, identifying regions of similarity that may indicate functional, structural, or evolutionary relationships. They work on improving its algorithms, enhancing user interface, fixing bugs, and updating the software to meet the evolving needs of the bioinformatics community. They also provide technical support, create documentation, and often collaborate with researchers to incorporate new scientific findings into the software.