A "principal investigator" is the person in charge or leading a research project or study. They are responsible for planning and managing the project, overseeing the research team, and ensuring the objectives are met. Full definition
She was principal investigator of a local research team for the national Early Head Start Research and Evaluation Project. (products.brookespublishing.com)
He served as principal investigator for the first rigorous, nationwide examination of the effectiveness of nonprofit charter - school management organizations. (edimpactlab.com)
If you work in a university department you're likely to be part of a research team and, as your career progresses, you may become principal investigator leading a team. (prospects.ac.uk)