On April 21, 1967 a group of 4 colonels of the Greek army took control of Greece through a military coup. The leader was a man named George Papadopoulos.
During the 3 years before the coup the polictical situation in Greece was very unstable. The left wing radicals were gaining strength and there was considerable public unrest with almost daily demonstrations, strikes, and riots. The civilian government seemed to be incapable of controlling the situation which worsened day after day.
The colonels got together and formulated a plan which involved arresting all the Generals, politicians, and all other persons they felt who might be a threat to their military takeover.
They executed their plan late at night and caught everyone by surprise while they slept and without firing a single shot.
They then declared that the country was under marshall law and George Papadopoulos appointed himself Prime Minister and regent to the crown. The other colonels were all appointed to high positions in the government.
The dictatorship lasted for 7 years and it was indeed a totalitarian regime which placed significant limitations to individual's rights. Free elections were suspended. They made it illegal to strike, to demonstrate, to talk against the government, and to congregate for any purpose except for church.
Despite these limitations on freedom most Greeks were not particularly affected in a negative way. In fact, most Greeks profited from a quickly growing economy under the Colonel's military rule. By eliminating the parliament and most other cumbersome bureaucratic institutions the dictators were able to make decisions quickly and efficiently which helped streamline the functioning of the economy. This lead to economic growth and prosperity in Greece which has never been seen before or after.
Eventualy, though, their lack of political expertise and their refusal to restore democracy lead to their downfall.
For more I recommend Matt Barrett's History of Greece
Regards from Athens, Tom Mazarakis