Gustaf Axel Estlander (18 September 1876 – 1 December 1930) was a Finnish architect and one of the most successful Scandinavian yacht designers of the early 20th century.

He founded the architectural firm of Estlander & Settergren, which in 1903–1915 designed a score of large apartment buildings in the booming capital city of Helsinki.

His own enormous 150m² Skerry cruiser Singoalla reached 14.1 knots on a race from Kiel to Travemünde on the Baltic Sea, according to Uffa Fox, the well-known author on yacht design.

In the 1920s, Gustaf Estlander reached international fame as a yacht designer, obtaining six-metre commissions from as far away as Cuba and Singapore.

Estlander had himself participated in the 1912 Olympic regatta in Nynäshamn, Sweden, gaining a 4th place skippering his Fife-designed 8mR yacht Örn.