In 1921, the two friends approached Halfdan Christensen, who was manager at the National Theater in Oslo, to be employed as actors in the ensemble.

[2] Frogg made a positive impression, and he debuted in the role of the priest's son Benedikt in Nini Roll Anker's Kirken in the spring of 1921,[1] while Borgen went on to study law.

He also played Captain Stanhope in the R. C. Sherriff's Journey's End from 1928, about four days in the trenches during the First World War.

After the 27th performance, he died after falling from the veranda of his apartment on the eighth floor of a dormitory building at Frogner plass.

[16] They were the parents of the sculptor and Morgenbladet journalist Lise Frogg (1929–1958), who married the Danish architect Ulf Vejlby.