Vladimir Arnold
One of the world's most prolific mathematicians in the field of Mechanics. His career dates from Stalinist USSR, and he is still active at the turn of the 20th century. One of his earliest achievements is the Kolmogorov-Arnold-Moser Theorem in dynamics. Arnold's writing style mixes rigorous and abstract mathematics with informal, almost conversational prose. Arnold espouses a geometric approach to mathematics in general, and mechanics in particular. His opinions on the subject can be found on the web.
Arnold works at the Steklov Mathematical Institute in Moscow and at the University of Paris IX.