Francis Collins, director of the National Institutes of Health, will be stepping down from his position by the end of the year, the agency announced Tuesday.

Collins is the longest-serving presidentially appointed director, having served in the position for 12 years across three presidential administrations.

“It has been an incredible privilege to lead this great agency for more than a decade,” Collins said in a statement. “I fundamentally believe, however, that no single person should serve in the position too long, and that it’s time to bring in a new scientist to lead the NIH into the future.”