Diakos was born on the island of Chalki in the Dodecanese. He left the Italian-occupied Dodecanese in 1929 for Athens. Upon graduating Military School in 1934, he was commisioned a Sublieutenant in the Greek Army. At the outbreak of World War II he was a lieutenant commanding the 2nd platoon of the the I/4 battalion. He was among the first to see action and fell on Tsouka Hill, on November 1, 1940, fighting the Italian invaders of Greece.