Jan Cornelisz Vermeyen, or Jan Mayo, or Barbalonga (c. 1500 – 1559) was a Dutch Northern Renaissance painter.

According to Karel van Mander he was born in Beverwijk in 1500 and was honored for his career in the service of Charles V. He was a friend of Jan van Scorel and his portrait was engraved by Jan Wierix for Dominicus Lampsonius.

Vermeyen was a painter and tapestry designer, probably a pupil of Jan Gossaert. About 1525 he became court painter to Margaret of Austria, regent of the Netherlands, aunt of Holy Roman Emperor Charles V at Mechelen and in 1535 he accompanied the Emperor Charles V, the nephew of the Archduchess, at the Conquest of Tunis. He "designed a set of twelve tapestries commemorating scenes from the campaign that would travel with Charles wherever he went, to bear witness to this triumph." The still existing painting of the Hafsid King of Tunis Moulay Hassan, whom Charles re-instated on his throne after ridding the city of the pirate Hayreddin Barbarossa, was painted by Vermeyen while there.

This journey supplied him with scenes for later works, including tapestries designed in 1545/48 for Charles V's sister Regent of Hungary, Mary of Hungary. He died in Brussels. 

Many portraits are ascribed to him on very little evidence, according to modern scholars. He was followed by Willem de Pannemaker and Jan van Hemessen.