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Olga was born to Ernst and Mimmi (née Norlander) in 1917. She married Sven Dahl, who was a professor of geography at Gothenburg School of Business, Economics and Law before his death in 1979. Together they had four children: Östen, born in 1945; Gudrun, born in 1948; Ingolf, born in 1950; and Åslög, born in 1955.
Olga Dahl received her bachelor's degree in philosophy from Lund University. She then went to Gothenburg to begin studying family history, during which time she published a series of articles. In the late 1970s she wrote a book about Gothenburg, Göteborgs hjärta – en bok om människor, affärer och byggnader kring Kungsgatan (The Heart of Gothenburg - a book about people, things, and buildings around Kungsgatan), with several others, including Per Clemensson, who wrote about the period 1775-1875, and Sven Gulin, who edited and wrote about the 1600s and 1700s.
On her 90th birthday she witnessed her crowning achievement with the public opening of a database, "Göteborgs tomtägare 1637-1807", which details around 900 properties around Gothenburg and their owners over the two century period.
Olga was a member of the Gothenburg Regional genealogical society from the 1950s onward, and was a local writer for the Swedish Biographical Dictionary.