Fritz_Haber, his inventions killed millions and his invention (Haber–Bosch process) helps to produce food for billions.

" It is estimated that a third of annual global food production uses ammonia from the Haber–Bosch process, and that this food supports nearly half the world's population. "

https://en.wikipedia.org/wiki/Fritz_Haber

" Ammonia production is a highly energy intensive process consuming around 1.8% of global energy output each year (steam methane reforming accounts for over 80% of the energy required) and producing as a result about 500 million tonnes of carbon dioxide (about 1.8% of global carbon dioxide emissions) "

https://royalsociety.org/news-resources/projects/low-carbon-...