He is referred to as the Senior Scientist and never as the First Scientist (outside of the credits)
Talk about it here.
The Senior Scientist and another Sensorite scientist worked to cure John of the madness caused by the Sensorites' telepathic attacks on his mind.
Biography[[edit] | [edit source]]
The Senior Scientist and his colleague were recognized by a swirling pattern insignia on their chests. He and the other scientist later helped the First Doctor test the water on the Sense Sphere for poison, specifically atropine. When they found the poison, they helped the Doctor to develop an antidote.
He showed the Doctor to their aqueduct, and later showed Ian Chesterton and Susan Foreman the way to the aqueduct to rescue the Doctor. When the Doctor, Ian and Susan returned from the aqueduct, the Senior Scientist showed them the various items left behind by the humans who had visited the Sense-Sphere ten years previously. (TV: The Sensorites)