Willy Brandt was the much-admired initiator of Ostpolitik (trying to get Communist East Europe to behave like normal neighbors), mayor of Berlin during the Berlin crisis, and later Chancellor of Germany. He resigned after it was discovered that his personal assistant was a spy for the East German secret service, Stasi.
Brandt's real name was Herbert Frahm, but Herbert-Frahm-Platz doesn't have the same ring.