Quaternion
The quaternion number system, first described by William Rowan Hamilton in 1843, extends the complex numbers.
A quaternion usually takes the form:
$a + bi + cj + dk$
Where $a,b,c,d$ are real coefficients of $1,i,j,k$.
$\displaystyle i^2 = j^2 = k^2 = ijk = -1$
$q = (w,x,y,z)$