Gabriel (von) Hackl (24 March 1843 – 5 June 1926) was a German historicist painter.
A surgeon's son, he attended the gymnasium in his home town and the city school in Graz.
To fulfil his father's wishes he then studied anatomy, archaeology and drawing at the University of Vienna.
In 1865 he moved to Munich, at whose Akademie der Bildenden Künste he studied under Alexander Wagner and Carl Theodor von Piloty.
The Luitpold-Gruppe also included Hugo Bürgel (its president), Walter Firle, Fritz Baer, Karl Marr, Johann Sperl and Wilhelm Leibl.