Johann Jakob Pfeiffer (6 October 1740 – 26 November 1791) was a German evangelical theologian, as well as a professor, and later, dean, at the University of Marburg.

[3] In 1779, Pfeiffer was named director of the newly constructed Lyceum Fridericianum, but by December of that year, he had been appointed associate professor of Theology at the University of Marburg, replacing Heinrich Otto Duysing.

In addition to his duties as Dean and Professor, he also served as a Councilor of the Consistory, overseeing all evangelical protestant churches in the Landgraviate of Hesse-Cassel.

[8][4] Two months later, despite the ministrations of his colleague Christian Friedrich Michaelis, he died due to complications from a chronic inflammatory illness, from which he had suffered for many years.

[11][12][13] Together they had the following children:[14] Lucie Pfeiffer died giving birth to twin sons, Franz Georg and Christian Hartmann.