After Surinamese independence in 1975, he also received Surinamese nationality. He would live there for 50 years, his entire active life. Mulder was known as a 'youth priest' and as a 'media priest' appearing on Radio Apintie and since 1966 STVS. He was important for the development of several sports in Suriname and was chairman of the Suriname Volleyball Association. He was also a long-distance runner. During the 1980 Surinamese coup d'état, when no newspapers were published, he wrote critical articles in the church magazine "Omhoog".