Get this Quaternion Package from Maple's Application Center. Make sure you get the March 2007 version not the March 2005 version.

Overview on Hamilton Quaternions

A Hamilton Quaternion is a hypercomplex number with one real part (the scalar) and three imaginary parts (the vector).

This is an extension of the concept of numbers. We have found that a real number is a one-part number that can be represented on a number line and a complex number is a two-part number that can be represented on a plane. Extending that logic, we have also found that we can produce more numbers by adding more parts.
Quaternion --> a + b*i + c*j + d*k, where the coefficients a, b, c, d are elements of the reals