This is the individual who is in charge of the day-to-day functions of the research project, including protocol for how research and data collection activities are completed. The Research Director works very closely with the Principal Investigator, and both (or all, if there are multiple PIs) report on the research.
 
Specifically, this individual designs all guidelines, refines and redirects any protocol as needed, acts as the manager of the team in regards to time and budget, and evaluates the progress of the project. The Research Director also makes sure that the project is in compliance with all guidelines, including federal and institutional review board regulations. They also usually assist the PI in writing the research articles related to the project, and report directly to the PI.