Count Hermann-Karl von Keyserling (1697–1764) was a Russian diplomat from the Keyserlingk family of Baltic German nobility based in the Duchy of Courland and Semigallia.
In 1733, the nobility of Courland sent Keyserling to Saint Petersburg in order to inform Ernst Johann von Biron that he had been elected Duke of Courland. Biron was so pleased with the news that he had Keyserlingk appointed President of the Saint Petersburg Academy of Sciences.
A year later, Keyserling was appointed Ambassador of the Russian Empire at the court of August III in Dresden and Warsaw. He kept this position until his death. As the Russian ambassador to the imperial court in Vienna he was made an imperial count in 1744.
Johann Sebastian Bach, a noted composer, is thought to have composed the Goldberg Variations for Count Keyserling as a sleep aid. The work takes its name from Johann Gottlieb Goldberg, a musician in the service of Count Keyserling.
His son Heinrich Christian von Keyserling was the wealthiest aristocrat of Konigsberg whose palace was frequented by the likes of Immanuel Kant and Johann Gottfried Herder. His marriage to Caroline von Keyserling was childless.
Herman Karl's daughter Anna von Medem was the great grandmother of geologist Alexander Keyserling.