This individual is quoted in several books but without biographical details other than his own accounts of his military service. He serves in the Prussian Army, then with the Brunswick Hussars, a campaign or two with the KGL in the Peninsula (1810/1811?) followed and by 1812 he had left the British Army and was with the Pavlograd Hussars. In 1815 he is serving in the Prussian Army again, possibly as a cavalryman, where he meets Bluecher.
Soldiers of fortune are notorious for their remarkable and fictional accounts of their careers e.g. the CSA Gemeral StLeger Grenfell, Captain "Watt Whalley" of the Zulu War, Lockhart Wishart, the Austrian General, veteran of the SYW who claimed he had had fought for Shah Nadir (a Scot, his family estate is 300m from my own house), a slew of French mercenaries in India in the 18th and 19th centuries. 20th century mercenaries before Britain and France entered the WW2 conflict claimed service in the Chaco War, Spanish Civil War, Sino-Japanese War and Finland. Mostly with very doubtful credentials.
This chap seems genuine but the details are so vague and his reason for leaving the KGL to serve in Russia obscure. The other transfers follow a pattern of an anti-Napoleon soldier. Any contributions to the solution of this mystery are welcome.
I should note that surely service in the Pavlograd Hussars required a knowledge of Russian? A knowledge of French and English might be considered possible as a minor gentleman (he is still only a troop leader after seven or eight years military service) but where would he acquire a knowledge of Russian. Perhaps he is from East Prussia?