The Duke and Duchess of Boxford are people featured in the Thomas the Tank Engine and Friends TV Series. They visited the Island of Sodor once, and brought their private engine Spencer the Silver Bullet Engine, who boasted to Gordon but then ran out of water on Gordon's Hill. Later they bought a holiday home on the Island, and had Edward the Blue Engine take their furniture car, who beat Spencer to the house. The Duke and Duchess now visit regularly, to see the wonderful and useful railway.
The Duke and Duchess were introduced in 'Gordon and Spencer' in Season 7, but were not seen until the Season 8 story 'Edward the Great'. They haven't appeared since.