Sigurd Frosterus (1876-1956) was a Finnish architect, art critic and art collector.
Frosterus graduated in Helsinki University in history of art in 1899, and got a diploma of architecture in 1902.
In 1920 he became a doctor with dissertation about use of colour in art.Frosterus had an architecture studio 1902-1904 with Gustaf Strengell and in 1918-1935 with Ole Gripenberg.
Frosterus and Strengell drew villas and manor houses, including Tamminiemi, which later became one of the official residences of the President of Finland from 1940 until 1981.The most well known work by Frosterus is Stockmann department store in Helsinki.
The architecture competition was held in 1916, but the building was finished only in 1930.Frosterus inspired numerous Finnish artists with his art theories and criticism.
He collected post-impressionist art.Frosterus was the editor of Arkkitehti magazine 1908-1911, and published books about art theory.