After having played a variety of roles, founded Ko Arnoldi in 1933 along with Jan Musch and Else Mauhs theatre company the mask on. Here he translated his first pieces from the French and Italian. From the forties Arnoldi was connected with the Rotterdam-based people's University, where he provided the drama class.
Ko Arnoldi founded In 1947 the Rotterdam Theatre , a theatre company including Hans Balan and John Leddy were joined. Ko van Dijk sr. got given big roles in this company by Arnoldi, and become known to the general public.  in addition to scene was Arnoldi especially in the last years of his life, to see more often in movies, on television and he was in several radio plays. In 1949 he was appointed officer of the order of Orange Nassau.
Arnoldi was married to actress Mary Servaes (1880-1966).
- Tomorrow is going to better! (1939)
- For Thursday evening twelve hours Mylord (1957)
- The case of the core (1961)
- Like two drops of water (1963)