Peter (Petter) Jacob Hjelm (2 October 1746 – 7 October 1813) was a Swedish chemist and the first person to isolate the element molybdenum in 1781, four years after its discovery by Swedish chemist Carl Wilhelm Scheele. Working with Molybdic acid, Hjelm chemically reduced molybdenum oxide with carbon in an oxygen-free atmosphere, resulting in carbon dioxide and a near-pure dark metal powder to which he gave the name 'molybdenum'. His first publication on molybdenum appeared in 1790.