Adelphi

A Time Lord messenger or The Messenger came to Earth to warn the newly exiled Third Doctor about events.

The Time Lord first met the Third Doctor when he appeared in his TARDIS while the Doctor was with his companion Liz Shaw. (AUDIO: Shadow of the Past)

This Time Lord was sent by the Time Lords to tell the Doctor that the Master had arrived on Earth. He also warned him of an impending trap that the Master had set for the Doctor. When the Doctor asked for assistance in dealing with the trap, however, this Time Lord simply disappeared. (TV: Terror of the Autons)

He was sent to see the Doctor again when he was with Sarah Jane Smith in order to persuade the Doctor not to travel with a future companion whom the Doctor had not yet taken onboard the TARDIS. (PROSE: An Overture Too Early)

Appearance
He was dressed as an English businessman, complete with bowler hat and umbrella. He compared his appearance to that of the Doctor's, stating that some Time Lords chose to remain inconspicuous. His disguise was somewhat compromised however, by his first being seen to hover in mid-air, due to his co-ordinates having "slipped". (TV: Terror of the Autons)