My career aim is to understand the water oxidising enzyme Photosystem II in terms of its mechanism, its assembly and its evolutionary relationships with other photosynthetic reaction centres. This enzyme has become the focus of attention because cheap water splitting catalysts are urgently needed in the energy sector for solar fuel production, electrolysis of water and the reverse reaction in fuel cells. My research has made major contributions to understanding this enzyme before it was either popular or profitable. Now that it is finally becoming both of those, I hope to continue to do more of the same. Not just because it might contribute to solving aspects of the energy crisis but also because understanding the enzyme, which put the energy into the biosphere, the oxygen into the atmosphere and thence changed the planet, is one of the greatest challenges in biology and chemistry. It is also a fun enzyme to work on.