Clarivate Analytics publishes the below list of Highly Cited Researchers (largely represented by STEM researchers).
The most well-known quantifier for researcher impact is the h-index. You can find a Researcher h-index in Web of Science, Scopus and Google Scholar databases. It is based on the number of citations publications have received and the total number of publications. Web of Science and Google Scholar can be accessed through the Chester Fritz Library.
Investigate Altmetrics & Researcher Profiles for alternative methods of measuring researcher impact.