3. Jamie McCrimmon/Zoe Heriot (The War Games)
I consider the exits of Jamie McCrimmon and Zoe Heriot to be the original versions of the Donna Noble departure as said earlier in this list. As the result of requesting the help of the Time Lords during The War Games, both Jamie and Zoe have their adventures with the Doctor wiped from their memories and are deposited back at points just prior to when they would have first met him. It's a rather sad thing to do, as Jamie is one of my favourite early companions he brought some real life to the role and I would love to see another Scotsman be one of the Doctor's companions once again. Jamie came back for the Two Doctors (as well as the Five Doctors but in a misleading appearance that relied on his original departure for a resolution). As far as I'm concerned, the departure of Jamie and Zoe were an attempt to one-up the departure of Susan. It also cleared the slate in preparation for Jon Pertwee's third Doctor. Jamie in particular had been in more adventures than any other companion at that point a total of 21 episodes. In fact, only Billie Piper as Rose Tyler has equalled it, with the 50th anniversary episode will go to 22 episodes and become the most frequently used companion of all times. So consider if you will, if next week, everything that Rose ever did was completely undone and she was sent back to a department store in 2005 with no idea who the Doctor was. That would be effectively what happened to Jamie and Zoe.