J. Heinrich Matthaei (born 4 May 1929 in Bonn) is a German biochemist. He is best known for his unique contribution to solving the genetic code on 15 May 1961. Whilst a post-doctoral visitor in the laboratory of Marshall Warren Nirenberg at the NIH in Bethesda, Maryland, he discovered that a synthetic RNA polynucleotide, composed of a repeating uridylic acid residue, coded for a polypeptide chain encoding just one kind of amino acid, phenylalanine.