Willem Leonard Oltmans (10 June 1925 – 30 September 2004) was a Dutch investigative journalist and author who did not hesitate to pro-actively intervene in international politics.

Due to the highly critical and opposite stance he often took towards Dutch global politics, as of 1956 the Dutch government conspired to keep him out of work. A lengthy lawsuit (1991–2000) involving the Royal family led to the state having to pay him damages. An erudite orator, the straightforward and uncompromising Oltmans was a striking character in Dutch society.