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
Galois:
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Galois
Cauchy:
https://mathshistory.st-andrews.ac.uk/Biographies/Cauchy
Fourier:
https://mathshistory.st-andrews.ac.uk/Biographies/Fourier