Hendrik Pieter Nicolaas Muller, GON, RNL, FRGS (2 April 1859 in Rotterdam - 11 August 1941 in The Hague, Netherlands) was a Dutch businessman, diplomat, world traveller, publicist, and philanthropist. He was a son of Hendrik Muller Sz., a Rotterdam-based Dutch businessman and politician, and Marie Cornelie van Rijckevorsel, member of another prominent Rotterdam based business family.
Muller started his career as a businessman, trading with East and West Africa. In his mid-twenties he travelled to Zanzibar, Mozambique, and South Africa for business purposes, but showed himself a keen ethnographer as well, collecting ethnographic artifacts and writing reports about the societies and people he encountered on his way. In 1890, Muller retired from business for personal reasons, and went to Germany to study ethnography and geography. He graduated with a Ph.D. dissertation four years later.
In 1896 he was first appointed consul and later consul general for the Orange Free State. Muller held this position all through the Second Boer War and his high-profiled performance as European representative for this Boer republic won him considerable fame and notoriety, which lasted all his life. After the Treaty of Vereeniging was signed in 1902 Muller retired to a life of travelling and writing for some years, making Muller a household name with his travelbooks. In 1919 the Dutch government appointed him envoy extraordinary and minister plenipotentiary to Romania, and later to Czechoslovakia, where he retired in 1932. As diplomat Muller strongly promoted Dutch business interests, especially in oil and electrotechnics.
Muller was a prolific writer. Over the course of his life he published well over two hundred articles, brochures, and books about his travels through the world, about South Africa and the Boers, and about Dutch foreign policy and diplomacy, apart from a range of other subjects. Muller gathered a large fortune with well appointed private investments. He bequeathed his considerable wealth to a private fund in support of academic research and cultural heritage.