Archibald (or 'Archie' for short) was a member of a large group of space pirates who attempted to invade and destroy the Starship Brilliant in the 40th century. Archibald was the junior member of the crew, working alongside teammates Dashiel and Jocelyn. He appeared to be the youngest of the group, sometimes acting like a stroppy teenager when in the presence of Dashiel. Their pod flew in ahead of the rest of the pirate's fleet, as Dashiel wanted to get the best spoils from the ship. As it was, they landed before the time loop came into action, trapping them aboard the ship.
Archibald seemed scruffy and cruel to begin with, but after talking with Martha Jones, it became clear that he had an unsure, simple personality, and that he would prefer a nice life to a pirating one. He later attempted to convince the rest of the pirates to come round to his way of thinking, but his attempts were in vain. He was shot by Captain Florence on board the main pirate ship, but came back to life thanks to the Doctor, who has increased the size of the time loop to include the main pirate ship as well as the Brilliant.
His fate after the events of the pirate attack are unknown. After the Doctor successfully convinced the pirates to join him on the Brilliant for a party, Archie was among those dancing on board. When the Doctor offered to either take them home or leave them in the time loop, Archie's decision (and everybody else's) remained a mystery.
The name of Archibald's species is also up for debate - they were referred to in the book only as Human Badgers, due to their badger-like appearance. It is also possible that the actual species name is 'Space Pirate'. (NSA: The Pirate Loop)