Toomas Hendrik Ilves
Toomas Hendrik Ilves CC '75 served as the President of Estonia. While at Columbia he majored in psychology. He was rumored to be attempting to implement aspects of Columbia's Core Curriculum (which he still waxes nostalgic about on Twitter) in the education system in Estonia, although his role as president was mostly ceremonial.
In 2007, he returned for the World Leaders Forum. He apparently liked to take Estonian academics out to the West End whenever he was in town, though it's not certain what he's up to now that it's gone.