User:SOTO/Forum Archive/The Panopticon/@comment-24070818-20131124143458/@comment-188432-20131126200056

...Or indeed the Sixth Doctor in season 21. The key is that they have recurred at some point. They needn't recur within that season to be classed as recurring. So the Brig in season 13 and season 26, or Cassandra O'Brien.Δ17 in series 1 and 2 are "recurring characters".