A tsolias is a Greek soldier wearing a military uniform based on a traditional Greek guerrilla outfit from the 19th century's Greek War of Independence. The foustanella (skirt) is based on the ancient Greek tunic called a chiton. The red fez hat is a vestiage of Turkish occupation. The first King of Modern Greece, Otto wore this uniform often in public. Today, many Greek boys dress up as tsoliades on Greek Independence Day (March 25th).
In Athens today, the Tsolias is a soldier that serves in the Presidential Guard. Although their role is mostly ceremonial, such as guarding the Tomb of the Unknown Soldier (shown here) they are usually selected from the Greek special forces and are therefore skilled fighters too. It is a great honor to be selected to serve here. Via Alitisa's description