Johan Castberg was a Norwegian jurist and politician best known for representing the Radical People's Party. He was a government minister from 1908 to 1910 and 1913 to 1914, and also served seven terms in the Norwegian Parliament. The brother-in-law of Katti Anker Møller, the two were responsible for implementing the highly progressive Castberg laws, granting rights to children born out of wedlock. Altogether, he was one of the most influential politicians in the early 20th century Norway.
In 2013, an oilfield in the Barents Sea was named after Johan Castberg.