Rotors are construct in geometric algebra to represent rotation. It generalizes complex numbers and quaternion but can even works on higher dimensions. Even though 3D rotors and quaternions are isomorphic, rotors are easier to visualize and does not require a fourth dimension or stereographic projection.
A rotor
View the note on geometric product for more information.
This is analogous to the quaternion, where to perform a rotation we need to apply a quaternion and its conjugate: