Conrad Johann Matthiessen (25 July 1751 – 23 January 1822) was a leading Hamburg merchant and banker during the French Revolutionary Wars.
Among the women in the group his closer friends included Elise Reimarus, Magdalena Pauli and the writer-poet Elisa von der Recke who describes him in her diary as a "pure, noble and beautiful soul ... better suited for Heaven than for Earth".
He was a member and regular presence at the "Monday Society", founded in 1784 by Friedrich Gottlieb Klopstock and Johann Georg Büsch.
In July 1790 he was one of approximately eighty leading Hamburg intellectuals who took part in the "Revolution Festival" arranged by Sieveking and held in a pub garden at Harvestehude to celebrate the first anniversary of the Storming of the Bastille.
[1] In 1793 Matthisen joined with two of his friends to buy a country house beside the Elbe at Neumühlen, a half hour's walk to the west of Altona, on a piece of land today known as Donners Park.