Jan Baptist van Helmont, Flemish chemist and physician (d. 1644)
Jan Baptist van Helmont (; Dutch: [ˈɦɛlmɔnt]; 12 January 1580 – 30 December 1644) was a chemist, physiologist, and physician from Brussels. He worked during the years just after Paracelsus and the rise of iatrochemistry, and is sometimes considered to be "the founder of pneumatic chemistry". Van Helmont is remembered today largely for his ideas on spontaneous generation, his 5-year willow tree experiment, and his introduction of the word "gas" (from the Greek word chaos) into the vocabulary of science.

His name is also found rendered as Jan-Baptiste van Helmont, Johannes Baptista van Helmont, Johann Baptista von Helmont, Joan Baptista van Helmont, and other minor variants switching between von and van.