Lieutenant Jan Olieslagers was a Belgian motorcycle and aviation pioneer who set world records with both types of machinery.

Lieutenant Jan Olieslagers turned in his bicycle to become an early motorcycle speed record holder; he was the first to go 100 kilometers (62 mi) per hour, and was 1902 World Champion.

At the time, he was flying a Nieuport 10 dubbed le Demon, which was the only craft in the Belgian air force painted with camouflage markings and the outside circle of the roundels inscribed in black.

[3] Olieslagers seems to have begun 1917 with a newer Nieuport, but with two more unconfirmed victories in his newly acquired Hanriot HD.1.

[3] As if Olieslagers' poor record of approvals was not sufficient to keep his score low, he also habitually took the fight to the Germans and was indifferent to the paperwork to staking claims.

[2] Jan Olieslagers seldom took leave, although he did visit Colonel Isaac Newton Lewis, the machine gun inventor, in London on many occasions.

He habitually broke in rookie pilots, cushioning their entry into the deadly art of aerial warfare.

The combination usually meant a reliable airplane under the ace, but on 9 November 1918, engine problems brought Jan Olieslagers down in a field near Eeklo.