Count Carl Gustav Rehnskiöld (6 August 1651 - 29 January 1722) was a Swedish Field Marshal under the command of King Charles XII of Sweden. Despite being choleric and irritable, Rehnskiöld's military skills made him the chief military advisor and second-in-command to King Charles and earned him the epithet, the "Parmenio of the Northern Alexander."
During his life, he played an important role in the Great Northern War. He commanded at the Battle of Fraustadt, after which King Charles XII made him a Field Marshal and Count. Highlights of his career include a highly successful campaign against Poland from 1701-1703, and the disastrous Ukrainian campaign which ended with the Battle of Poltava in 1709. The Battle was a disaster for the Swedish army and Rehnskiöld was captured by the Russians. He remained in Russian captivity until 1718.
One of the most successful Swedish Generals of his time, he nonetheless paved the way for the rise of Russian military power, and the fall of the Swedish military might.