Zundapp KS601 with Steib Sidecar
Zündapp (aka Zuendapp) was a major German motorcycle manufacturer founded in 1917 in Nuremberg. After WWII, the company transitioned to smaller machines, notably the "Bella" motor scooter, which was a relatively heavy machine for its type. In 1951, Zündapp released the last of its heavy motorcycle models, but one of its most famous was the KS601, the "Green Elephant," with a 598cc two-cylinder engine.
Source: Mecum Auctions as part of the Houston auction in April, 2014