In this lecture I answer a very trivial sounding question. Why do we name the three basic unit vectors - the ones directed along the coordinate axes - i, j and k? What's in a name, you ask? Well - history, mostly! I describe how, motivated by phase factors rotating points on an Argand plane, Hamilton tried to generalize complex numbers, which can be described by a pair of real numbers, to triplets of real numbers. Failing that, he realized that quartets of real numbers - with three imaginary units, rather than just one, will do just what he wanted. Thus quaternions were born. I then go on to describe pure quaternions - which were what ultimately morphed into vectors in the hands of Gibbs and Heaviside. I end with a discussion on how quaternions can be used to rotate vectors in three dimensional space.
