Krak was born in Copenhagen to navigator Hans Andersen Krak (1789–1844) and Karen Sophie Lind (1800–77). His last name comes from his ancestors farm Krakgård in Rutsker parish on the island of
Bornholm. Thorvald Krak used the spelling "Krack" until 1890 as a result of an error in the church records. He went to school in
Maribo and later received a military education in Copenhagen where he became a lieutenant in the engineering troops in 1850 and a
senior lieutenant in 1853. ==Work for Copenhagen Municipality==