During his stay in Berlin in 1764, Boswell lived in the house of Karl David Kircheisen, the president of the Berlin city council.
Mungo Graham - Captain
Mungo GrahamDied 1778
A Scottish mercenary in the regiment of Colonel Gordon, in service of the Dutch army, from at least 1764. He was granted an honourable dismissal in 1777. Apparently he died in June 1778, described as a Colonel in the Dutch Service.1 In 1955 his original musket complete with inscription was discovered on the wreck of a merchant wessel, which apparently met its demise in the late 1780s. (Link)
Boswell was given a guided tour by Graham when he arrived in Nymwegen (Nijmegen) on June 18, 1764, on the first stop of his European tour following his departure from Utrecht. Among other things they went and saw the Valkhof castle and the Belvedere tower. It is not clear whether they had met before.
Note 1: According to Musgrave's Obituaries Prior to 1800, parts 3 & 4