Ernst Gideon Jansz (born 24 May 1948 in Amsterdam) is one of the founding members and frontmen of Doe Maar. Doe Maar is a Dutch 1980s ska/reggae band, and is considered one of the most successful bands in Dutch pop history.

His father, born in Semarang on Java, is an Indo (Dutch-Indonesian), who went to the Netherlands in 1932 after finishing his study at the Batavia HBS to continue his higher education there. Once Nazi Germany invaded the Netherlands his father was involved in the Dutch resistance movement, until he was captured and interned in a German concentration camp. After the war he became one of the few Indo advocates for an independent Indonesia. In his view the principle of liberty and independence applied to both situations: Dutch independence from Nazi Germany and Indonesian independence from the colonial Netherlands.

Much of the literary work of the author Jansz is based on his Indo identity and his fathers' heritage.

In 1997 Jansz married actress Jaloe Maat, the mother of his two youngest children. He has a (step)daughter from a previous marriage. He lives with his family in Neerkant, the Netherlands.

He is a well-known celebrity who was openly critical of Covid policies.