When someone mentions the TARDIS team, most fans' first thought is likely to be of a Doctor and his companion or companions. For example, the team of Eleven, Amy and Rory, or Five, Nyssa, Tegan and Adric. However, there have been a number of characters who pop up every now and again as enemies or allies who augment this team. One of the most famous examples of this during the Classic Series was the Brigadier, who first appeared alongside the Second Doctor and then had adventures with Four, Five and Seven as well as being a series regular during the Third Doctor's reign.
However, having lots of returning characters has been especially true of the new series. This is thanks to a number of reasons, most notably the companions' families getting a stronger focus in the Russell T Davies years, the groups of the Doctor's allies cropping up during Steven Moffat's time in charge and the recurring allies from both eras of the show.
Each recurring character has added something extra to the show that has helped it to rise to its current popularity. As such, many have become firm fan favourites and here's our defintive countdown of 10 of the very best so far, analysing just what makes them so appealing.