During his stay in Berlin in 1764, Boswell lived in the house of Karl David Kircheisen, the president of the Berlin city council.
Gerhard Christiaan Rücker
Professor of law at Utrecht University (around 1760).
Possibly the Johann Gerhard Christian Rücker (1722-1780) who was sometime professor at Groningen.1
Life with Boswell:
Boswell went to Rücker's lecture on September 20, 1763, before settling on following Professor Trotz's lectures instead.