Hans Fruhstorfer was a German explorer, insect trader and entomologist who specialised in Lepidoptera. He collected and described new species of exotic butterflies, especially in Adalbert Seitz's Macrolepidoptera of the World. He is best known for his work on the butterflies of Java.
His career began in 1888 when he spent two years in Brazil. The expedition was financially successful and led to his becoming a professional collector. Next he spent some time in Sri Lanka, then in 1890 he went to Java for three years, visiting Sumatra. Between 1895 and 1896 he collected in Sulawesi, Lombok and Bali. In 1899, he went on a three-year journey to the United States, Oceania, Japan, China, Tonkin, Annam and Siam, returning via India.
Following his travels, he settled in Geneva where he wrote monographs based on the specimens in his extensive private collection. Many of these were incorporated into Seitz's work. In taxonomy he made extensive use of the structure of the male genitalia. Fruhstorfer, in these years also studied Palearctic butterflies, Orthoptera and botany. No longer travelling himself, Fruhstorfer employed the collectors Hans Sauter in Formosa and Franz Werner in New Guinea.