Warrien

Warrien was a representative of his home galaxy at the first meeting of the Galactic Council which allied with the Daleks in their plan to conquer the Solar System. Warrien wore a protective pressure suit and appeared to have a human face beneath his cowled helmet. He disappeared from later meetings, his place taken by Celation. (TV: Mission to the Unknown)

Behind the scenes
The actor who played Warrien did not receive a credit. However, Johnny Clayton and Len Russell played 'Alien Delegates', while Pat Gorman played a 'Planetarian'. It remains unclear, to date, which of these actors played the character.