An RWR Mark II was a type of android.
The Entity had one guarding a grey door as part of a test for the Doctor. The Entity summoned the first seven incarnations of the Doctor, one at a time in reverse order. Each one managed to get past the android, but were pushed through the door into another dimension by an impostor posing as their companion. The First Doctor, however, deduced the truth, allowing the fake companion to fall through the door instead. He therefore passed the test. (AUDIO: Seven to One)