Karl Janssen (29 May 1855 — 2 December 1927) was a German sculptor working in the Baroque revival tradition; he was born and died in Düsseldorf. Born in a family of artists, he studied at the Königlich Preußischen Kunstakademie in Düsseldorf from 1872 to 1880. In 1878 he garnered a scholarship to study in Rome; he remained in Italy from 1881 to 1884.
On his return his first notable commission was for a memorial portrait bust of the industrialist Poensgen (1883) for his monument in the Nordfriedhof, Poensgen (1883) für dessen Erbbegräbnis auf dem Nordfriedhof.
In 1884, together with Josef Tüshaus (1851–1901), whom he had known from their days at the Akademie, he was commissioned to produce a sculptured group for the visit to the city by Kaiser Wilhelm, on the theme of Father Rhine and his Daughters. The result so pleased Düsseldorfers that in 1897 Janssen and Tüshaus were requested to cast a more durable version in bronze, for a city fountain (illustrated).
The previous year (1896), he cast the equestrian statue of Kaiser Wilhelm, lost in the Second World War.
Since 1893 he had been teaching as a professor, taking the chair of the late August Wittig. Among his outstanding pupils were Frédéric Coubillier and Wilhelm Lehmbruck.
Following the First World War he was commissioned by Henkel to sculpt a war memorial to fallen Henkel workers, to be erected at the Henkel works in Düsseldorf-Holthausen. His last well-known work was also for the Henkel family, a mourning figure in Art Deco style for the family mausoleum (1925).