Quaternions, an extension of complex numbers, have practical applications in physics, particularly in 3D modeling, satellite attitude control, and computer graphics, where they help avoid singularities associated with Eulerian rotations. They were discovered by Sir William Rowan Hamilton in 1844 and are often compared to 4-vectors in modern physics, with discussions highlighting their advantages and limitations. While quaternions can perform similar functions to 4-vectors, they are specifically designed for four-dimensional space. Resources for learning about quaternions include books like "Quaternions and Rotation Sequences" by JB Kuipers, which covers both mathematics and applications. Overall, quaternions play a significant role in various fields, demonstrating their importance in both theoretical and applied physics.