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.

However, he never identifies himself by name within Death Comes to Time itself, instead introducing himself as "the Brigadier" much as Renegade Time Lords might call themselves simply "the Doctor" or "the Master". Given how much else Death Comes to Time rewrites about the backstory of the Doctor, it is impossible to confirm, in-universe, how similar this Brigadier was to the Alistair Gordon Lethbridge-Stewart of the Doctor's universe.