First check who was chancellor in 1990.
All four people offered were federal chancellors, but at different times. The connection to 1990 distinguishes Kohl from his predecessors and successor. Their shared first name Helmut does not distinguish Kohl from Schmidt.
After the Wall opened, Kohl presented a ten-point programme in the Bundestag on 28 November 1989. It proposed steps towards German unity. The later epithet refers to this political context and to the unity ultimately achieved.
The other three answers
The other chancellors governed outside the decisive year.
Gerhard Schröder
Gerhard Schröder became chancellor in 1998, after reunification. He is not the person meant by this epithet.
Konrad Adenauer
Konrad Adenauer was chancellor from 1949 to 1963. His term belongs to the early Federal Republic, not to reunification in 1990.
Helmut Schmidt
Helmut Schmidt governed from 1974 to 1982. Remember the surname: Helmut Kohl, not Helmut Schmidt, held office in 1990.
An epithet is not a complete explanation of reunification.
Protests by people in the GDR, political change across Europe and negotiations with international partners were also decisive. The epithet recognises Kohl’s role without erasing those other contributions.
The Wall’s opening and reunification have different dates: 9 November 1989 and 3 October 1990. An explanation of the epithet should not treat them as one day.
Helmut Kohl, 1982–1998 · Federal Chancellery ↗Kohl – chancellor in 1990 – Chancellor of Unity.
This three-part connection checks the name, term of office and historical context together.
Three words for this question
- der Beinameepithet
- An additional name connecting a person with a quality or achievement.
- die Amtszeitterm of office
- The period during which someone holds an office.
- die Wiedervereinigungreunification
- The establishment of German state unity in 1990.