Short answers, pulled from the story.
Ostpolitik was a strategy to normalize relations between West Germany and Eastern Europe through rapprochement. This approach challenged the Hallstein Doctrine by engaging communist governments instead of isolating them.
Chancellor Willy Brandt signed the Treaty of Moscow in August 1970. The agreement renounced the use of force and recognized current European borders.
Egon Bahr proposed change through rapprochement as a strategy to improve life behind the Iron Curtain during a speech at the Evangelische Akademie Tutzing in 1963. His ideas eventually reshaped European foreign policy under Chancellor Willy Brandt.
Helmut Kohl assumed power in 1982 but maintained the core principles of Ostpolitik despite his earlier opposition. He continued the path laid out by Willy Brandt, evidenced by Erich Honecker's visit to West Germany in 1987.
South Korea adopted a similar approach called Nordpolitik in the 1980s named explicitly in allusion to Brandt's work. This policy aimed at rapprochement between North and South Korea using strategies inspired by West German diplomacy.