Theodor Haagaas

Theodor Christian Petersen Haagaas
Theodor Haagaas, 1911
Born	(1873-06-15)June 15, 1873 Tistedalen
Died	December 25, 1961(1961-12-25) (aged 88) Oslo
Resting place	Vestre gravlund 59°55′55″N 10°42′06″E / 59.931924°N 10.701681°E / 59.931924; 10.701681
Nationality	Norwegian
Occupation	Educator and private school owner
Awards	King's Medal of Merit in Gold (1949)

Theodor Christian Petersen Haagaas (15 June 1873, Tistedalen – 25 December 1961, Oslo) was a Norwegian mathematician, private school owner, author and officer in the Royal Norwegian Navy. He was a co-owner of Frogner School and Nissen's Girls' School (1913–1918) and founder, owner and headmaster of the Haagaas School, a private gymnasium at Frogner, Oslo that existed 1915–1955. He is also known for the widely used Haffner og Haagaas series of textbooks in mathematics, which was published between 1925 and 1979 in numerous editions. He received the King's Medal of Merit in Gold in 1949.

He grew up in Tistedalen outside Frederikshald. His parents were Theodor Christian Haagaas (1823–1899), a ship-owner and managing director (1862–1892) of the sawmills of Saugbrugsforeningen, Norway's largest timber company, and Nora Martha Petersen (1845–1887), who was born in Eidsfoss to Swedish-born parents from Värmland of at least partially Forest Finnish descent. His maternal grandfather owned Veden Manor in Tistedalen for some years. Theodor Haagaas was one of the pioneers of skiing in Tistedalen around 1885–1886.

In 1908, he married Henriette Wegner Paus (1879–1942), a daughter of the theologian and private school owner Bernhard Pauss and of the teacher and editor Henriette Wegner; she was a granddaughter of the industrialist Benjamin Wegner and of Berenberg Bank co-owner Henriette Seyler. They had four daughters, among them the humanist and World War II resistance member Henriette Bie Lorentzen. Theodor Haagaas was the maternal grandfather of the civil servant Joakim (Theodor Haagaas) Lystad.