The 15th iteration of everyone's favorite Timelord is going to be played by Ncuti Gatwa in Doctor Who's fourteenth series. However, fans also know that the actor will be accompanied by a brand-new companion known as Ruby Sunday. The Doctor's companions are an integral part of Doctor Who, and many people have flown in the TARDIS alongside The Doctor. Some of these previous companions have passed on and will not be seen again. However, some of these characters have simply retired from traveling in space and time.