This equation, set out by William Rowan Hamilton, is central to an obscure branch of mathematics called quaternion algebra. The video above explains what it means.
"The story is that Hamilton came up with this equation whilst walking in Dublin, and he carved it on a bridge in triumph," says Chris Budd of the University of Bath in the UK.
Nowadays, quaternion algebra is central to the computer graphics industry. It is used to describe the orientations of objects on the screen.
Read more: What is the most beautiful equation?