I understand that Ose learned the monte on the street during the days when he was wrestling with the bottle. Later, he weaned himself off the bottle and became an officer in the Salvation Army.
Somebody brought Ose to the Larsen brothers to show his stuff, and suggested that Ose act as the house magician in exchange for an apartment in the Castle, at which he would double as night watchman. In those days, there was lots of space there in the Castle, as it was largely undeveloped both financially and architecturally.
The Larsens were quite nervous to set a reformed alcoholic loose in the Castle night after night with an unlimited supply of booze, but they were finally convinced to take a chance.
Obviously, Ose did not disappoint anyone. He became an unforgettable fixture there at the Castle and never strayed from the straight and narrow.
Or so the story goes.