Possible Clues:

• Irishman or Welshman, e.g.
• KG or Big Baby
• Breton, e.g.
• Welshman or Irishwoman, e.g.
• Invader of Rome in 390 B.C.
• Ancient European
• Cornishman or Welshman
• Stonehenge builder
• Boston cager, informally
• Ancient Briton or Gaul