In biographies, August von Goethe (1789-1830) was the son of German polymath Johann Goethe, the only one of the five children, of the paring of Christiane Vulpius (1765-1816) and Goethe, to reach adulthood, who was notably present at their 19 October 1806 wedding (see: Goethe timeline), and, as it has tentatively been argued, the embodiment of many of the regrettable aspects of the Otto child in Goethe’s 1809 Elective Affinities (see: Goethe’s affinity table).
Ottilie von Goethe | Offspring
In 1817, August Goethe married Ottilie Pogwisch (1796-1872), "Ottilie von Goethe" thereafter, the daughter of a countess who arrived in Weimar in 1806, soon becoming good friends with Adele Schopenhauer (1797-1849), sister of Arthur Schopenhauer (1788-1860), daughter of Johanna Schopenhauer (1766-1838), the women in whose home Goethe and his new scandalous bride Christiane made their first public appearance.
The marriage, said to have been a problematic one, produced three children: Walter Wolfgang von Goethe (1818-1885), Maximilian Wolfgang von Goethe (1820-1883), and Sedina Alma Henrietta Cornelia von Goethe (1827-1844), none of whom produced offspring. 
It may be that some aspects of Ottilie von Goethe may have fused into the character of "Ottilie" of Goethe's 1809 Elective Affinities, although this is only speculation, at the moment (fact check).
August, towards his end, was said to have turned to alcohol, which may have played a role in his early death on a trip to Rome, age 40, in 1830; an Italian trip which seems to echo that made by both his father and grandfather, at about the same age.
1. Ottilie von Goethe (German → English) – Wikipedia.
● August von Goethe (German → English) – Wikipedia.