[1] He enrolled in an art school in Vienna; however, with the outbreak of World War I, he was drafted into the Austro-Hungarian army.
[2] After his recovery, he was called to the front; however, he was found to be overwhelmed by his war experience and sent to a military insane hospital in Trnava.
[2] He began his career as a caricaturist by drawing caricatures of the statesmen who attended the Paris Peace Conference in 1919.
[4] There, in collaboration with another Hungarian Jew, Alois Derso, he worked for fifteen years at the League of Nations in Geneva.
[4][5] Their work, signed as Kelen-Derso, appeared in numerous European newspapers and gained global recognition.