An American named John Ledyard is the…
August 1788 CE
He had traveled around the world with Captain Cook and been acquainted with Thomas Jefferson before attempting a voyage across Russia, Siberia, and North America.
Having failed to complete his journey, he called on Sir Joseph and the African Association, who thought him a perfect fit for their enterprise.
After setting sail from England on June 30, 1788, he arrives in August at Cairo.
While preparing for his westward journey inland in search of the Niger, however, he falls ill and, trying to relieve his "bilious complaint", inadvertently poisons himself with a fatal dose of sulfuric acid.