Otto Graef was born about 1861 and studied the trades of watchmaker and jeweler. In 1889, after visiting La Chaux-de-Fonds the young Graef decided to stay in the city thanks to the well-paid work he found there. Initially an independent watchmaker, his firm grew into MIMO, also called Graef & Co]].
In 1928 Graef seized the opportunity to purchase a controlling stake in Girard-Perregaux, one of the most successful watchmakers in the city. He merged this with MIMO and continued growing the firm, acquiring new clientele and an international reputation through the 1930s and 1940s.