The word 'protein' is derived from the Greek word 'proteios', which means 'primary' or 'first'. This term was first used in the 1830s by the Swedish chemist Jöns Jacob Berzelius to describe the nitrogenous compounds found in plants and animals. Berzelius believed that these compounds were the essential constituents of living organisms and that they were responsible for their unique properties. He named them 'protein' ('pro-tein') from the Greek root 'proteios' to reflect their importance.