And not long afterwards, Clifford generalized real numbers, complex numbers, and quaternions into what are now known as "Clifford algebras". Handy stuff. Certain algebras allow you to express geometric shapes such as points and lines using very simple equations. Other algebras show how quaternions (for example) arise naturally as the even subalgebra of Cl0,3(R). The "spacetime algebra" appears as CL1,3(R), which makes it easy to express special relativity.