Otto Bærentzen started in business as an apprentice in the James Petersen & Co. firm, and then took over the company 10 years later. He later started several companies of his own, including the København Machine Business, Deutsche-Nordische Exportgesellschaft, and Dobel & Co. Bærentzen took part as a fencer at both the 1920 and 1928 Olympics. Both his son and daughter later competed at the Olympics in fencing. He was a big financial supporter of sport, especially fencing and rowing. After his wife’s death, Bærentzen donated their large villa in Lyngby to the local authorities, who converted it into a retirement home.