Jan van Oort (13 April 1921 – 29 November 2006) was a Dutch children's book writer and comic strip cartoonist, working under the pseudonym of Jean Dulieu (French pronunciation: [ʒɑ̃ dyljø]).

[1] He was the son of concert singer Hendrik C. van Oort, and grandson of the political cartoonist Johan Braakensiek.

[2] Jan van Oort studied the violin on the conservatorium where he graduated in 1940, and became violinist with the Amsterdam Royal Concertgebouw Orchestra.

[2][3] Shortly after the war, Van Oort and his family moved to Terschelling, and a year later ended his participation in the orchestra, aiming for a full job in comics strips, although having no education in this field.

In September of that year, his daughter Dorinde van Oort published a novel about her family, where her father is named Lepel Mansborg.

Starting 1967, Van Oort made 39 puppet movies of 10 minutes each for the Dutch television programme Monitor.