King Gustaf VI Adolf of Sweden, in his posh Mercedes-Benz 300 Cabriolet D (W186)
Series W186 was the first true luxury car in Germany after World War II. The model was called often as Adenauer, because the first chancellor of BRD loved this technically advanced vehicle. But - as you can see - the 300 was popular among other statesmen, too.
By the way, the Cadillac behind the Mercedes-Benz is also noteworthy. It was sixteen years old, when the photo was taken in 1955.