Robert McNeill (Neill) Alexander, CBE FRS was a British zoologist and a leading authority in the field of biomechanics. For thirty years he was Professor of Zoology at the University of Leeds.

Biomechanics is the study of the structure, function and motion of the mechanical aspects of biological systems, at any level from whole organisms to organs, cells and cell organelles, using the methods of mechanics. Biomechanics is a branch of biophysics.