Belsazar de la Motte Hacquet, (also Balthasar or Balthazar Hacquet) (1739 - January 10, 1815) was an Austrian physician and scientist born in Le Conquet, France.
He studied in Vienna, and was a surgeon during the Seven Years' War. Later he was an instructor of anatomy and natural sciences in Laibach (now Ljubljana), and in 1788 was a professor at the University of Lemberg. After 1810 he lived in Vienna.
Hacquet is remembered for his scientific journeys throughout the Austrian Empire. He was a polymath, and performed research in the fields of geology, mineralogy, botany, chemistry, ethnography, petrology and karstology. He is recognized as the first scientist to perform extensive exploration of the Julian Alps. In 1777 he was the first to try to ascend to the top of Triglav (2864 m), the highest peak in Slovenia, and reached Mali Triglav (2725 m).
Among his written works is the four-volume Oryctographia Carniolica, which included a geological and mineralogical study of Carniola, Istria, and surrounding districts. This work also included an in-depth report of the Idrija mercury mine. He also wrote an ethnographical study of Southern Slavic peoples in a treatise called Slavus Venedus Illyricus.
As a botanist Hacquet wrote a book on alpine flora from Carniola called Plantae alpinae Carniolicae. The botanical genus Hacquetia epipactis is named after him, as well as the plant species Pedicularis hacquetii (Hacquet's lousewort). On one of his excursions, he discovered "on the evening, Trenta side of Triglav, a new species of scabious" and picked it for his herbarium collection, nowadays preserved in the Natural History Museum of Slovenia. He called the species Scabiosa trenta in the published description, and drew it. Many botanists have sought the mysterious pale yellow scabious, among them also the young Julius Kugy. He searched for the secretive flower, and though he was not able to find it, this led him to became a great explorer and describer of the Julian Alps. The Austrian botanist, A. Kerner, later proved Belsazar Hacquet had not found a new species, but a specimen of the already known submediterranean Cephalaria leucantha.