[6] He frequently appeared in movies and television series and worked with the likes of Axel Corti and Alan J. Pakula (Sophie's Choice).

He is well known for his chilling role in that film as the SS physician forcing Sophie to choose which one of her two children would be gassed and which would proceed to the labor camp.

He made a name of himself as playing females, as in La Cage aux Folles at Volkstheater, one of his signature roles.

[10] In 2003, Hackl was diagnosed with a malignant brain tumor, but recovered and returned to the stage in 2005, also appearing in different films and series.

In 2009 he published a book about his cancer and the long process of recovery[11] and also recorded a CD with cover versions of songs from Austrian singer Georg Danzer.