Although we have absolutely no documentation as to how Haydn made the acquaintance of his father-in-law, Pohl assumed that Haydn was introduced to the wigmaker's family by Keller's brother Georg Ignaz Keller, a musician at St. Stephen's, whom Haydn had known since his days as choirboy at the Cathedral. Georg Ignaz Keller was born around 1699 in the Bohemian town of Chlumec nad Cidlinou and came to Vienna before 1726 as an employee of the Bohemian Court Chancellor Leopold Count Kinsky, for whom he served as chamberlain and violinist. Therefore Haydn scholarship universally assumed that Haydn's father-in-law also hailed from Bohemia. In his article "Joseph Haydns Jugendliebe" (Innsbruck, 1956) Ernst Fritz Schmid vividly describes Georg Ignaz Keller's progress as a musician in Vienna and how he rose from a simple servant to a violinist at St. Stephen's Cathedral in 1731 and a court musician in 1765. In spite of complete lack of evidence Schmid presents the family relationship between the "Keller brothers" as fact:
Der kaiserliche Hofmusikus Georg Ignaz Keller ist es nun gewesen, der Haydn die Bekanntschaft mit der Familie seiner Jugendliebe und damit auch seiner späteren Frau vermittelte. Kellers älterer Bruder, der "hofbefreite" Perückenmacher Johann Peter Keller, der um 1691 ebenfalls in Chlumetz in Böhmen geboren war, besaß zu Wien in der Vorstadt Landstraße in der Ungargasse ein eigenes Haus und einigen Wohlstand [...] Georg Ignaz Keller brachte Haydn in das Haus des Bruders, wo mehrere Kinder, darunter anmutige Töchter heranwuchsen, deren Klavierunterricht der junge Meister übernahm.
This is the official marriage record on which Haydn scholarship in general and Ernst Fritz Schmid in particular always relied. But the sparseness of the entries in the marriage records of St. Michael's has a special reason: there's an - unfortunately not complete - series of "Verkündbücher", i.e. records of the basic personal information that the parish priests wrote down, when the engaged couple first appeared and announced their intention of getting married and the banns were to be published. The entry pertaining to Johann Peter Keller's wedding is (as was regularly the case with these first and only provisional entries that were to be crossed out later) much more detailed. Among other information - such as the date of the first announcement and the couple's address - it gives Johann Peter Keller as being of German origin, having been born in Hamburg:
Den 31 October 1722 copulati sunt 12 9ber 1722 / Der Kunstreiche Herr Johann Peter Keller, ein Keÿ[serlich] Hofbefreiter Porakhenmacher, b ei dem / 3 tauben in der unde[r]n Preinerstrasen wonhaft. / Zu Hamburg gebirtig, des H[errn] Johann Georg Keller, undt Frau Aloysia sel[ig] beder / ehlicher Sohnn. nimbt zur ehe die tugent / same Jungfrau Mariam Elisabetham / Seillerin, des H[errn] Georgij Seiller und Elisabethæ sel beder eheliche tochtor / Zu Wacheram in Österreich gebürtig, / beÿ den 3 taube[n] in der under / Preinerstrass wonhaft. / 1 2 3 Ambo in parochia / per plures annos.
Approaching the end of his life Johann Peter Keller suffered hard times, which in a fascinating way may reflect the demise of the wig as a social and economic factor. He died on 9 August 1771, absolutely destitute in the "Klerfisches Haus" on the Hoher Markt and was buried the following day in the new crypt of St. Stephen's. His relatively wealthy children (and maybe his son-in-law) made sure that his 3rd-class funeral cost 27 fl 36 x and even comprised a "Music vors Miserere" for 4 Gulden.