Georgios Siantos (nicknames: Geros "Old man", Theios "Uncle"; Greek: Γεώργιος "Γιώργης" Σιάντος; 1890 – 20 May 1947) was a prominent figure of the Communist Party of Greece (Greek: Κομμουνιστικό Κόμμα Ελλάδας, romanized: Kommunistiko Komma Elladas, KKE) who served as acting general secretary of the party, and as a leader of the National Liberation Front (EAM)/Greek People's Liberation Army (ELAS) Resistance movement during the German occupation of Greece in World War II.
During the internal ideological struggle of 1929–1931, Siantos as a leading member of the "left faction" was called to Moscow, where he accepted the admonitions of Comintern for unity in KKE.
After his return to Greece, Siantos participated in the administration of General Confederation of Greek Workers, and in 1934 he was reelected in the central committee and the politburo of the party.
The same year representatives from all political parties and resistance groups came together at a conference in Lebanon, seeking an agreement about a government of national unity.
[3] In February 1945 Siantos led the delegation of KKE and EAM that negotiated the Treaty of Varkiza with the Greek government and the other political parties.