Karl Theodor Otto Christian August Bayrhoffer (14 October 1812, in Marburg – 3 February 1888) was a German American philosopher, free-thinker, and publicist.

Afterward he became a champion of German Catholicism and wrote Researches into the Essence, History, and Criticism of Religion (1849).

From 1846 through 1849 Bayrhoffer was suspended three times from the university for unlawful behavior related to his activities as a German Catholic dissident.

[1] A passionate free-thinker and religious activist, he then founded the free-religious movement as part of the Friends of Light (or "Lichtfreunde") in Marburg in 1847.

"While the Majority in June was creating an Imperial Regent, these men had held a great meeting of their own party in Frankfort, brought together by Professor Bayrhoffer of Marburg, a dapper little man with a sharp nose and a thin voice, who hitherto had never known anything of the world outside of Hegel's Logic, and who now became, quite as exclusively, a votary of the theories of Robespierre.

It was decided to unite the countless Democratic societies into one large well-organized Association under one common direction, to keep the people in as continual a state of restlessness as possible, and in all conceivable ways to prepare for one last great blow.

[2] The result of which was a counter-revolutionary response via suspension of the constitution by Elector Friedrich Wilhelm I, the dissolution of the Diet, and an unsuccessful declaration of martial law.

Upon declaration, 241 of 277 Kurhessian officers submitted dismissal applications because of their oath not only to the electorate but also to the constitution which the assembly upheld.

They sailed to the United States by way of England and settled in Jordan, Wisconsin where he purchased a farm.