The venerable elderly gentleman in the painting by Andreas Scheppelin is Johann Wolfgang Textor, Goethe’s maternal grandfather, in his 70s at the time. As town mayor he was the highest official of the Free Imperial City of Frankfurt and representative of the emperor. He is depicted wearing his official attire and with a gold chain and medallion.

He spoke little, and never showed a trace of vehemence; I do not remember ever having seen him angry. [...] What increased our respect for this worthy old man to the highest degree, however, was our conviction that he possessed the gift of prophecy, especially in matters pertaining to himself and his destiny.

Goethe: From My Life. Poetry and Truth, part 1 , book 1