He went to Sweden in 1631 with the Scottish troops brought over by the Marquis of Hamilton, and was in 1651 created Baron Skalby, and in 1654 COUNT OF SKENNINGE.
He was a Scottish cavalry general during the Thirty Years' War rising to the rank of Field Marshal (1657–1662) in the Swedish-Polish wars.
He served between 1658-1661 as military governor of Estonia and Livonia. In 1660, he and the Swedes took Jacob, Duke of Courland as their prisoner. He also led the Swedish forces in the conquests of Valmiera and Mitau.
https://www.wikitree.com/wiki/Douglas-6231