The Examiner (The Power of the Daleks)

The Examiner was an official sent from Earth to the colony on Vulcan after Quinn had alerted Earth to the threat of a rebellion on the planet.

Biography
While the Examiner was waiting for someone from the colony to meet him, he encountered the Second Doctor, who was newly arrived on the planet. The Examiner started to introduce himself to the Doctor, but then suddenly was shot and killed by an unseen assassin.

The Doctor found the Examiner's official badge, but while examining it he was attacked by the assassin. During the struggle, the Doctor managed to pull a button off the assassin's clothes before being knocked unconscious. The Doctor then assumed the Examiner's identity, hoping to expose the murderer. The body of the real Examiner was later found in the mercury swamp. (TV: The Power of the Daleks)