Complex sentence: Luce de Gast (or Luces de Gast) born c.1190, lord of the castle of Gast, near Salisbury; reputed author of the first part of the French poem, Tristan.
Split into simpler sentences: Luce de Gast (or Luces de Gast) born c.1190, was lord of the castle of Gast, near Salisbury. He is the reputed author of the first part of the French poem, Tristan.