One of the most exciting episodes of palaeoanthropology was the find of the first transitional form, the Pithecanthropus erectus, by the Dutchman Eugène Dubois in Java during 1891-1892. The history of Dubois and his finds of the molar, skullcap and femur, forming his transitional form, are described. Besides the human remains, Dubois made a large collection of vertebrate fossils, mostly of mammals, now united in the so-called Dubois Collection. This collection played an important role in unravelling the biostratigraphy and chronostratigraphy of Java. Questions, such as from where were those mammals coming, when did Homo erectus arrive in Java, and when did it become extinct, and when did Homo sapiens reach Java, are discussed.