Hugo Reinhold Karl Johann Höppener, known as Fidus, was born the son of a confectioner. He demonstrated artistic talent at an early age. Around 1886 he met the "apostle of nature", artist Karl Wilhelm Diefenbach, and joined his commune near Munich. On Diefenbach's behalf, he served a brief prison sentence for public nudity, earning him the name nickname Fidus or "the faithful".

In 1892 he moved to Berlin, set up another commune, and worked as an illustrator on the magazine Sphinx. His work appeared frequently in Jugend and other illustrated magazines. He created ornamental drawings, especially for book decoration, as well as ex-libris, posters and designs. He also contributed to the early homosexual magazine Der Eigene, published by Adolf Brand.

Fidus held theosophical beliefs and during the 1890's he became very interested in German mythology. His engravings evoked an insular worldview with an internationalist outlook, which promoted many German artists long after 1900. He continued to work in the Art Nouveau style long after it was fashionable.

Hoppener was considered part of the German Secessionist Art Nouveau Movement and known as a symbolist to the world.. His ability to combine elements of mysticism, eroticism, Art Nouveau and Symbolism in a graphic style made him highly popular in his day, as well as, today.

Fidus was a forerunner in using his graphic works as postcards to advertise and sell his work. He described each of his postcards, and distributed the cards widely. It is not known just how successful he was in selling his works with the cards, but the cards themselves have become extremely popular with collectors today.

After 1918, interest in Fidus’ work as an illustrator waned and he was not received well by the Nazi regime. In 1937 his work was seized and the sale of his images was forbidden. By the time he died in 1948 his art had been almost forgotten. It was rediscovered in the 1960s, and directly influenced the psychedelic style of graphic design of posters which began to be produced around San Francisco.