Jovan Karamata was an outstanding mathematician who lived through the wars of the first half of the 20th century in the Balkans. He gained international fame with a 2-page proof of the Hardy-Littlewood theorem, and also did excellent work on slowly varying functions and on Tauberian theory.
Find out more at: https://mathshistory.st-andrews.ac.uk/Biographies/Karamata/