Wagner is a Knight of the Brotherhood of Steel (Eastern division) in 2287.
Knight Wagner was a part of a scouting mission to the C.I.T. ruins to look for an entrance to the Institute. Unbeknownst to them the intelligence was correct, however they sealed the entrance years ago - once they acquired their teleporter. They spent days meticulously combing through the ruin until they came they were boxed into an old tunnel by synths, wherein they took minor casualties. He would latter recommend following the trail back on whoever provided the intelligence. Commenting that "some wastelander is feeding Proctor Quinlan lies to earn some caps."
Wagner is mentioned only in Fallout 4.