The Valkyries, or Arcee Twins, is a small group of Autobots working for N.E.S.T..
Them being called twins is actually a popular misconception, as when the characters are introduced, the Major is talking about the Twins right after.
They participated in helping N.E.S.T and protecting Sam Witwicky, who carried the Matrix, from the Decepticons, so they could revives Optimus Prime. They were all killed in battle of Egypt, and a grave was made to honor their services. However, in an alternate timeline, they successfully captured their quarry, Sideways, and returned to their home after the resurrection of Cybertron.
