Wagner (School Reunion)
From Tardis Wiki, the free Doctor Who reference
Mr Wagner was one of Mr Finch's Krillitanes who took over the Deffry Vale High School in order solve the Skasas Paradigm and become "gods". All the Krillitanes were destroyed when K-9 blew up a can of their oil. (DW: School Reunion)
He is unique in the fact his true krillitane form is grey. He is the only one known to have this look.
