Theodoros Michopoulos, a close adviser to Prime Minister Alexis Tsipras, with a long history in Greek journalism, died in the early hours of Sunday of a heart attack at the age of 65.
With years of experience in both private and state television in Greece, Michopoulos became an adviser to Tsipras shortly after the leftist-led coalition took power after playing an active role in SYRIZA's election campaign.
He also worked closely with Finance Minister Euclid Tsakalotos and talks with representatives of Greece's international creditors.
Condolences were expressed across the political spectrum.
Tsipras's office described Michopoulos as "a dedicated leftist, a rare journalist and a wonderful person."
Parliament Speaker Nikos Voutsis called Michopoulos "an eminent journalist" as well as "a good friend, a conscientious comrade of the reformist, communist and broader radical left"
"During his long and distinguished career as a journalist, he was combative and consistent in his ideas for which he struggled until the end," conservative New Democracy said in a statement.