Sentreal

Sentreal was a representative of his home galaxy at the first meeting of the Galactic Council.

He had apparently been persuaded to join the alliance by Zephon. By remaining low-key at the meetings, he survived until the final meeting, where he strongly challenged Mavic Chen, and was then imprisoned by the Daleks. With Celation, Beaus, Mavic Chen and Malpha, the remaining members of the Council, he agreed to go back to his own people and warn them about the Daleks' invasion plans and to fight against them, upon their escape from Kembel. (TV: Mission to the Unknown, The Daleks' Master Plan)

Sentreal, a tall alien, his face indistinguishable due to the dark visor and chlorine fumes he breathed, wore a protective suit, and his helmet had an antenna on top. (TV: Mission to the Unknown, The Daleks' Master Plan)

Behind the scenes

 * The actor who played Sentreal in Mission to the Unknown did not receive a credit, but Sam Mansary played an "Alien Delegate", and is of African descent, which matches the still shots from the episode which appear to show a dark-skinned actor inside Sentreal's space suit.
 * Sentreal is shot and killed by Mavic Chen in the novelisation. In the televised story, Chen shoots Gearon, not Sentreal.