Newton

This is one of the best all around sites that I have found. It is titled “The MacTutor History of Mathematics Archive.”
http://www-history.mcs.st-and.ac.uk/~history

This is an award-winning site that links to all sorts of mathematics information.
https://mathshistory.st-andrews.ac.uk/HistTopics/History_overview

Isaac Newton:
https://mathshistory.st-andrews.ac.uk/Biographies/Newton.html… See the whole entry

This is one of the best all around sites that I have found. It is titled “The MacTutor History of Mathematics Archive.”
http://www-history.mcs.st-and.ac.uk/~history

This is an award-winning site that links to all sorts of mathematics information.
https://mathshistory.st-andrews.ac.uk/HistTopics/History_overview

Newton:
https://mathshistory.st-andrews.ac.uk/Biographies/Newton.html

Leibniz:… See the whole entry