William Justin Kroll was a Luxembourgish metallurgist. He is best known for inventing the Kroll process in 1940, which is used commercially to extract metallic titanium from ore.

Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in sea water, aqua regia, and chlorine.