Theo Paphitis owned the retail stationery chain Ryman.
Paphitis acquired Ryman, the British stationery retailer, and expanded his business interests through a retail group that also included other consumer brands. His experience in retail helped shape the commercial perspective he brought to Dragon's Den, where he assessed pitches involving products, distribution and customer demand.
Ryman is a specialist stationery and office-supplies chain with a long history in the United Kingdom. It should not be confused with WHSmith, Staples or Paperchase, which are separate businesses that have also operated in stationery and office retail. The question asks for the chain associated with Paphitis personally, not a retailer that appeared in a pitch.
Paphitis became a Dragon in the early series and was one of the original investors. His later public profile combined entrepreneurship, retail ownership and television work, but Ryman remains the clearest named retail business connected with him.