He chose his stage name after the elephant Kala Nag ("Black Snake") from Rudyard Kipling's Jungle Book.
Due to his good contacts to Propaganda Minister Joseph Goebbels he made his career at the Tobis Film Company.
Around this time he also helped produce the film "Robert and Bertram" the only anti-semitic musical comedy[4] released during the Nazi regime.
Schreiber got involved with the National Socialists as president of the Magic Circle (1936–1945), membership was reduced from the originally 1373 members to 400 and prevented the use of Jewish compositions as background music.
Schreiber became director of the Bavaria Film in Munich, produced public speeches by Adolf Hitler and in 1939 was a guest at the Berghof am Obersalzberg.
Schreiber fostered friendship with Hitler's personal adjutant, SS Gruppenführer Julius Schaub, who sponsored magical events.
Magicians and illusionists were accepted by the Nazi regime as long as they followed the regulations and the expression was for entertainment rather than an active belief in the occult .
Schreiber propagated the illusion "Simsalabim" as his creation,and said to have been inspired by the German children's song "Auf einem Baum ein Kuckuck saß" wherein the lyrics "Simsaladim" appears.
[6] Towards the end of the war, Schreiber mediated between the Allies and wanted SS men, who offered free access to the legendary stolen Nazi gold, which is officially largely lost.
After a denazification process, Schreiber fled to the British occupation zone to Hamburg, where he lived with a magic friend who was known as the "king of the black market" and was later convicted of diamond smuggling with a Swiss magician.
With the support of former Tobis people, he entertained British occupation soldiers with his Kalanag revue, consisting of elaborate illusions and lightly dressed showgirls.
The most famous numbers included, among others, the Magic Bar dating back to Jean Eugène Robert-Houdin and made famous by David Devant, where throughout the show out of a single pitcher different drinks were served on demand, as well as after special tricks saying "And we'll do it all with water from India" he poured a spurt of water out of a never-ending carafe onto the stage.
Magicians like Janos Bartl or Fredo Marvelli, whom Schreiber had badly harmed during the time of national socialism, called for the boycott of his shows.
The magic historian Richard Hatch points out that the traveled countries strikingly match the banknotes that had disappeared in 1945 with the Nazi gold.
In the mid-1950s, Schreiber moved from Hamburg to the Württemberg village of Fornsbach, where his cousin Margarete Sedlmayer owned land and ran a café.