Original Second Doctor

An incarnation of the Doctor was seen during the Fourth Doctor's mindbending contest with Morbius. (TV: The Brain of Morbius, AUDIO: Cold Fusion) According to one account this man was an incarnation of the Other, whom the First Doctor was an reincarnation. (PROSE: Lungbarrow)

behind the scenes
The face of this Doctor were first introduced in TV: The Brain of Morbius but it was not until AUDIO: Cold Fusion thirty years later, in 2016 thatthey were confirmed to be incarnations of the Doctor.