Complex I (NADH:ubiquinone oxidoreductase) is the largest enzyme in the respiratory chain, coupling the transfer of electrons from NADH to quinone with the translocation of protons across the membrane, which has central importance in providing energy for the cell. Complex I is known to share common ancestry with the Group 4 [NiFe]-hydrogenases, which are metalloenzymes that catalyse the reversible reduction of protons and electrons to hydrogen gas. The details of how a presumably [NiFe]-hydrogenase-like ancestor evolved into Complex I is an open and fascinating question. Progress toward answering this evolutionary question has been made by analysing Asgard archaea, which are the closest relatives of eukaryotes. AlphaFold2 multimer predicts that Asgard archaea metagenomes harbour [NiFe]-hydrogenase complexes, and these complexes have a structural architecture resembling that of Complex I. Investigation into if and how these novel [NiFe]-hydrogenases are “missing links” in the evolution of Complex I is ongoing.