Dark Matter, formerly identified as Madge Undersee, is a Tribute who participated in JER's Tournament. She is converted into a completely different person due to Yesare Dernes, Head of State of the Refined Union of Empartia.
Although Madge died in the District 12 bombings, Yesare Dernes was able to recover her ashes and reproduce an almost exact duplicate of her. However, Madge is not able to recognize the existence of Katniss Everdeen, Peeta Mellark, or Gale Hawthorne. She was coached separate from the rest of the Tributes by Yesare Dernes herself.
Creation of "Dark Matter"
After redesigning Madge Undersee, Yesare was able to give her a new persona called Dark Matter. Dark Matter was a very hostile Tribute, especially when she forged her rivalry with Sedra Alsypse, and became known as Career-grade material within hours. The shocking thing was, she received a lower Training Score than Sedra Alsypse (with Dark Matter at 91/96 and Sedra Alsypse at 93/96), and thus, swore to slay Sedra herself....