Wagner (School Reunion)

"Mr Wagner" was a Krillitane, a member of the Chosen Few following Brother Lassar who took over the Deffry Vale High School to solve the Skasis Paradigm and become "gods". Kenny briefly saw him in his true form, but Wagner spared his life for unclear reasons, merely telling him to leave. All the Krillitanes were destroyed when K9 Mark III blew up a can of their oil.

He differed from the others in that his true Krillitane form was grey. (TV: School Reunion)

Behind the scenes
In a deleted scene, Wagner claimed to a vegetarian. When Mrs Jackson offered him a rat, he claimed to have turned organic. This may explain why he spares Kenny's life in spite of Kenny seeing his true monstrous form.