Jacobus Henricus van ‘t Hoff (apparently, and unsurprisingly, more commonly referred to as ‘Henry’) was the first person to win the Nobel Prize in Chemistry in 1901. This was for his research on reaction rates and equilibria, which helped establish modern physical chemistry. He also jointly recognised the tetrahedral shape formed by bonds around carbon atoms. Find a more detailed biography here.
Josiah Gibbs carried out theoretical work, applying the concepts of thermodynamics to chemical reactions. Amongst chemists, probably his best-known contribution is Gibbs free energy, which allows predictions to be made about whether reactions are feasible or not. There’s further detail on his life and work here.