Baron Karl von Hasenauer (German: Karl Freiherr von Hasenauer [ˈhaːzənaʊɐ]) (20 July 1833 – 4 January 1894) was an important Austrian architect and key representative of the Historismus school.

He was also a student of August Sicard von Sicardsburg and Eduard van der Nüll.

[2] For his outstanding work, he was ennobled by Emperor Franz Joseph I in 1873, and made Freiherr, the equivalent of baron.

After a conflict with his former business partner Semper he managed the building of the Hofburg alone.

The conflict over attribution of their joint projects continues to this day between the supporters of Semper and Hasenauer.