Complex sentence: Adlon took over Carl Hiller's restaurant at the Unter den Linden boulevard, which during his management became the most exclusive restaurant of Berlin, and so Adlon became an important social figure in Germany.
Split into simpler sentences: Adlon took over Carl Hiller's restaurant at the Unter den Linden boulevard. During his management, it became the most exclusive restaurant of Berlin, and so Adlon became an important social figure in Germany.