Complex sentence: Jean Fouquet or Jehan Fouquet (1420-1481) was the most important French painter of the 15th century, a master of both panel painting and manuscript illumination.
Split into simpler sentences: Jean Fouquet or Jehan Fouquet (1420-1481) was a French painter. He is the most important French painter of the 15th century, mastering both large-scale painting and manuscript illumination.