Title: Cold War (1953–1962)
Content:  German regime procured and stockpiled building materials for the erection of the Berlin Wall. Although this extensive activity was widely known, few outside the small circle of Soviet and East German planners believed that East Germany would be sealed off. On June 15, 1961, two months before the construction of the Berlin Wall started, First Secretary of the Socialist Unity Party and Staatsrat chairman Walter Ulbricht stated in an international press conference, ''"Niemand hat die Absicht, eine Mauer zu errichten!" (No one has the intention to erect a wall)''. It was the first time the colloquial term Mauer (wall) had been used 
Title: Berlin Wall
Content:   On 15 June 1961, First Secretary of the Socialist Unity Party and GDR State Council chairman Walter Ulbricht stated in an international press conference, "Niemand hat die Absicht, eine Mauer zu errichten!" (No one has the intention of erecting a wall!). It was the first time the colloquial term Mauer (wall) had been used in this context. The transcript of a telephone call between Nikita Khrushchev and Ulbricht, on 1 August in the same year, suggests that the initiative for the construction of the Wall came from Khrushchev. However, other sources suggest that Khrushchev had initially been wary about building a wall, fearing negative Western reaction. Nevertheless, Ulbricht had pushed for a border closure for quite some time, arguing that East Germany's 
Title: Mikhail Pervukhin
Content:  Pervukhin discussed other problems as well, claiming that Ulbricht but also the East German leadership in general, were opposed to the Soviet Union's plan to improve relations with West Germany. When Khrushchev gave his approval to construct what would become the Berlin Wall, Pervukhin was the first to know. Ulbricht told Pervukhin of the need to create the East–West barrier at night, and he and Khrushchev would later agree to this. At the 22nd Party Congress in 1961, Pevurkhin lost his seat in the Central Committee. He was succeeded in his post as Soviet ambassador to East Germany by Peter Abrassimov at the end of 1962.
Title: Nikita Khrushchev
Content:  Walter Ulbricht to begin construction of what became known as the Berlin Wall, which would surround West Berlin. Construction preparations were made in great secrecy, and the border was sealed off in the early hours of Sunday, 13 August 1961, when most East German workers who earned hard currency by working in West Berlin would be at their homes. The wall was a propaganda disaster, and marked the end of Khrushchev's attempts to conclude a peace treaty among the Four Powers and the two German states. That treaty would not be signed until September 1990, as an immediate prelude to German reunification.
Title: Berlin Crisis of 1961
Content:   In early 1961, the East German government sought a way to stop its population leaving for the West. Walter Ulbricht, First Secretary of the Socialist Unity Party (SED) and Staatsrat chairman and thus East Germany's chief decision-maker, convinced the Soviet Union that force was necessary to stop this movement, although Berlin's four-power status required the allowance of free travel between zones and forbade the presence of German troops in Berlin. The East German government began stockpiling building materials for the erection of the Berlin Wall; this activity was widely known, but only a small circle of Soviet and East German planners believed that East Germans were aware of the purpose. This material included enough barbed wire to enclose 
Title: Berlin Wall
Content:  existence was at stake. Khrushchev had become emboldened upon seeing US president John F. Kennedy's youth and inexperience, which he considered a weakness. In the 1961 Vienna summit, Kennedy made the error of admitting that the US wouldn't actively oppose the building of a barrier. A feeling of miscalculation and failure immediately afterwards was admitted by Kennedy in a candid interview with New York Times columnist James "Scotty" Reston. On Saturday, 12 August 1961, the leaders of the GDR attended a garden party at a government guesthouse in Döllnsee, in a wooded area to the north of East Berlin. There, Ulbricht signed the order to close the border and erect a wall. At midnight, the police and units of the East German 
Title: Pyotr Abrassimov
Content:  August 1961 was naturally taken by the East Germans in full consultation with the Soviet ambassador. From the East German perspective The Wall represented a necessary desperate attempt to save the state which appeared to be in the process of losing its entire working age population. With Abrassimov as Soviet ambassador in Berlin, Walter Ulbricht, who had earlier enjoyed close relations with Soviet leader Josef Stalin, found he enjoyed far less direct contact with the Soviet leadership in Moscow. In 1963/64, when Ulbricht moved to control air traffic flying into West Berlin, it was Abrassimov who prevented the move. 
Title: United States Army Europe and Africa
Content:  in the city. In the early years, travel between the sectors was unrestricted. At the time Soviet premier Nikita Khrushchev announced in June 1961 that the Soviet Union was planning to conclude a peace treaty with the East German government, 3,000 East German refugees flowed daily into Berlin. Suddenly on the night of 12 August 1961, the Soviets closed the border crossing points and began to construct the Berlin Wall, isolating the three western sectors of the city both from East Germany and the Soviet sector, or East Berlin. In response, the United States deployed an additional armored cavalry regiment to 
Title: Berlin Crisis of 1961
Content:  Berlin. Approximately 32,000 combat and engineer troops were employed for the building of the Wall, after which the Border Police became responsible for manning and improving it. To discourage Western interference and perhaps control potential riots, the Soviet Army was present. Kennedy did not give in to angry demands for immediate action raised by West Berliners and their mayor, Willy Brandt. Instead, he sent vice president Lyndon B. Johnson together with Lucius D. Clay, the hero of the Berlin Airlift of 1948‒49, to West Berlin on August 19. They managed to calm the population and demonstrate symbolically the United States' solidarity with the city. On August 20, 1,500 additional GIs arrived in West Berlin. On 30 August 1961, in response to moves by the Soviet Union 
Title: Berlin Blockade
Content:  Millions of East Germans escaped to West Germany over East Germany, and Berlin became a major escape route. This led to major-power conflict over Berlin that stretched at least from 1946 to the construction of the Berlin wall in 1961. Dwight D. Eisenhower became US President in 1953 and Nikita Khrushchev became Soviet leader in 1958. Khrushchev tried to push Eisenhower on Berlin in 1958–59. The Soviets backed down when Eisenhower's resolve seemed to match that of Truman. When Eisenhower was replaced by Kennedy in 1961, Khrushchev tried again, with essentially the same result.

Question: who was the leader of the soviet union when the berlin wall was built?
Answer: Khrushchev.
Nikita Khrushchev.
Joseph Stalin.