Aris Velouchiotis (Άρης Βελουχιώτης), (1905-June 16 1945, real name Thanassis Klaras) was a prominent leader of the communist segment of Greek guerrilla resistance during World War II which was followed by the Greek Civil War.

Klaras was born in Lamia (Greece) in 1905. As a youth he participated in the leftist movement of his era and finally became a member of the Communist Party of Greece (KKE). During the Ioannis Metaxas dictatorship of the 1930s he was arrested and jailed in the Aegina prison. During his trial he escaped and joined the illegal mechanism of the Communist Party. He was arrested again in 1939, he was sent to the Corfu prison and stayed there until he signed a “statement of renouncement” of the Communist Party.

During the World War II he served as an artillery sergeant of the Greek army in the Albanian front (1940-1941) against Mussolini's army until the Nazi invasion and Greece’s surrender (April 1941).

In November 1941 Klaras was sent to Central Greece (Roumeli ) by the Communist Party in order to assess the capacity of the development of a guerrilla movement against the Nazis. His proposals were adopted by the party and consequently in January 1942 Klaras moved to the mountains in order to start setting up the guerrilla groups.

The first appearance of the partisans organized by Klaras was on the 7th of June 1942 in the village of Domnista (Evritania) in Central Greece. This was also the first time that he appeared under the alias Aris Velouchiotis. From this time on, he rose to prominence in the ELAS ("Greek Popular Liberation Army") forces, which he headed along with Stephanos Sarafis.

One of the most important operations of the Greek resistance movement, in which Velouchiotis and his fighters participated, in cooperation with Napoleon Zervas's Nationalist EDES resistance forces and British saboteurs, was the blasting of the Gorgopotamus bridge in Lamia (November 1942). Their success disrupted the replenishment of Rommel's German forces in Africa for several days, as the latter took place by means of the Thessaloniki-Athens railroad.

This was to be, however, the last operation to pit the communist-dominated ELAS organization on the same front with Greek Nationalist resistance forces, who favoured a return to constitutional parliamentary monarchy, as opposed to the communists' aspiration of imposing a Soviet-type communist regime in Greece.

In October 1944,the Nazis evacuated Greece, and legitimate government was reinstated under Georgios Papandreou, the leader of a "National Unity" government-in-exile during the period of German occupation in Greece. When the Varkiza agreement was signed to end clashes between EAM-ELAS communist insurgents and governmental forces, Aris Velouchiotis vehemently refused to comply and collided with the Communist Party of Greece (KKE) leadership, which accused him of Trotskyism and treachery, referencing his 1939 statement of renouncement and removing him from the party's member list.

Aris Velouchiotis moved again towards the mountains of Central Greece, in order to start an insurgency against the legitimate Greek Government and the British allies who supported them. Though most of his associates abandoned him, he continued to conduct guerilla war until, in June 1945, he fell into an ambush by nationalist anti-communist forces and was killed, along with his deputy-commander, during battle. With regards to his death, many theories have been set forth, among which the allegation that he committed suicide after being incapacitated during the battle.

To the Greek public, Aris Velouchiotis came to be a symbol of the Greek society's division during the civil war that followed the country's liberation from the Germans. Lionized as a hero of the communist cause by leftists, he has become the subject of a personality cult comparable only to those of Ernesto Che Guevara, Stalin and Mao, and deliberately perpetuated well into the 21st century by the Greek Left.

On the other hand, however, he has been seen with little sympathy by right-wingers and centrists alike, who charge him and the communist party with the perpetration of mass atrocities against rural populations seen as negative to their "socialist cause", attacks against non-communist resistance forces who did not fit into their plan of a future, Stalinist, post-war Greece, and insurgency against a legitimate democratic government after Greece had been liberated from the Nazis.