Benoit Mandelbrot was a Polish-French and American mathematician and polymath. Mandelbrot is particularly known for his contributions to fractal geometry, in particular the Mandelbrot set, which he discovered in 1979. He is also known for his contributions in Chaos Theory and many applied fields such as randomness in financial markets, information theory and fluid dynamics.
The correct pronunciation of Benoit Mandelbrot is buh-nwah MAN-del-broht.
His last name, Mandelbrot, is a Jewish last name and not French.
However, depending on the language he was speaking, Mandelbrot himself varied his pronunciation, pronouncing the "n" with a nasal "n" and a guttural "r", when speaking French. In any case, the "t" is not silent and the "o" is pronounced as slightly closed in all languages.
His first name, Benoit, is French and is therefore pronounced as buh-nwah, where the "e" is pronounced with an "uh" sound.