Baron Janez Vajkard Valvasor (also spelled Johann Weichert) (baptized on May 28, 1641 - died on September 19, 1693), was a Slovene nobleman, scholar, and polymath, member of the Royal Society.

Janez Vajkard Valvasor was born in May 1641 in Ljubljana, Slovenia to father Jernej and mother Ana Marija b. Ravbar.

The Valvasors resided in a family castle Medija near Izlake . Janez Vajkard's father died when he was ten years old. At the time he was already attending the Jesuit school in Ljubljana. Graduating in 1658 at the age of seventeen, he did not choose to continue his studies at a university but decided to broaden his horizons by meeting learned men on a journey across Europe. This journey lasted fourteen years and it even took him to northern Africa. During this period, he joined the army in the Austrian-Turkish war , where he became closely acquainted with the conditions in the region of Vojna Krajina (Borderland, German Militärgrenze) in Croatia.

Shortly after marrying Anna Rosina Grafenweger in 1672, Janez Vajkard acquired the Bogenšperk castle near Litija, where he arranged for a writing, drawing and printing workshop. Valvasor spent a fortune on writing and publishing books to the extent that towards the end of his life he was forced to sell the Bogenšperk Castle, his vast library and his collection of prints.

His extensive treatise on the hydrology of the intermittent Lake Cerknica won him the membership of the Royal Society in London in 1688. Valvasor was a pioneer of studying the karst phenomena.

His single most important work remains the monumental The Glory of the Duchy of Carniola (Die Ehre des Herzogthums Crain in German, Slava vojvodine Kranjske in Slovene), published 1689 in 15 tomes, totalling 3532 pages and including 528 illustrations and 24 appendices, which provides a vivid description of the Slovene lands of the time.

Valvasor died in September 1693 in Krško, and is buried in the family tomb near Izlake.