The Brigadier (Death Comes to Time)

The Brigadier worked for UNIT and aided the Seventh Doctor.

He managed to stop Tannis' invasion with the help of the Doctor. Ace later informed him of the Doctor's death.

The Kingmaker suggested that the Doctor's death and defeat may have only happened in that universe. (WC: Death Comes to Time)

Behind the scenes
This individual, who has the voice and likeness of Nicholas Courtney, is ostensibly the version of Alistair Gordon Lethbridge-Stewart who exists in the backstory of the webcast Death Comes to Time.