Simplify the following text for a Grade 11 native English-speaking person.
Original: A parallel universe version of the Cybermen appeared in the 2006 series ' two-part story , `` Rise of the Cybermen '' and `` The Age of Steel '' , and have been recurring villains in the revived series since .
Simplified: A parallel universe version of the Cybermen appeared in the 2006 series in the two-part story , `` Rise of the Cybermen '' and `` The Age of Steel '' they also appear in Army Of Ghosts and Doomsday .