Simplify the following text for a Grade 8 native English-speaking person.
Original: Dark Jedi is the name given in the Star Wars universe to fictional characters attuned to the Force and adept in its dark side . They exist by that name only in the Expanded Universe , including video games such as Star Wars : Knights of the Old Republic and the Jedi Knight series ; the term is never used in any of the six Star Wars films .
Simplified: In the fictional Star Wars universe , the Jedi or Jedi Knights are members of an old order , who use a power they call The Force .