Short answers, pulled from the story.
The border with West Berlin was officially closed on Sunday morning, the 13th of August 1961. This date became commonly referred to as Barbed Wire Sunday in Germany.
At least one hundred forty deaths occurred according to research groups, though official figures previously listed only ninety-eight killed individuals. Estimates regarding fatalities vary significantly with some claiming well above two hundred.
First Secretary Walter Ulbricht signed the order to close the border and build a wall at a government guesthouse north of East Berlin on Saturday, the 12th of August 1961. A telephone call transcript suggests Nikita Khrushchev initiated the project while Ulbricht pushed for closure.
More than thirteen thousand East German tourists escaped through Hungary to Austria after an open border gate was created based on Otto von Habsburg idea. This event set chain reaction events into motion that led to mass demonstrations throughout East Germany.
Full demolition began the 13th of June 1990 and concluded in 1994 according to official records. Three long sections remain standing today as historical memorials including the East Side Gallery along Spree River.