The mathematical study of symmetry is called group theory because it studies ‘groups’ of symmetry operations. Most of these groups can be deconstructed into simpler groups, but those that can’t I have called ‘atoms of symmetry’. Almost all atoms of symmetry fit into a table, but there are 26 exceptions, the largest of which is called The Monster. After its existence was predicted in 1973, and even before it was constructed seven years later, it had shown strange connections with other parts of mathematics. These so-called ‘moonshine’ connections were subsequently linked with the mathematics of string theory, a proposed way of combining gravity with quantum theory.