Rhea (Supergirl)

Rhea, Queen of Daxam is the mother of Mon-El and the main antagonist in Supergirl season 2. Having desperately searched for her son for so many years that once she and Lar have found him on Earth, she wanted Mon-El back so badly but when Kara refused to cooperate with her demands, Rhea becomes a ruthless enemy to the Girl of Steel and is now hell-bent on wanting to kill Supergirl and get her son back no matter how many innocent lives she will destroy and kill to do it. She even killed her own husband. She manipulates Lena Luthor to build a machine to transport all daxamites to ruling Earth as New Daxam.

Even when Supergirl challenged Rhea to a duel in accordance to ancient Daxamite ways (with the wager that if Supergirl won the Daxamites would leave Earth forever otherwise Earth would surrender and Supergirl would no longer interfere) Rhea made it clear no matter what she would never honor any agreement as she ordered her army to attack the city and target places like schools and hospitals.

In the end, Supergirl (using a device given to her by Lena Luthor) made Earth uninhabitable to Daxamites by seeding the atmosphere with lead dust (lead being deadly poison to Daxamites). Her army fled for their lives and while Rhea lay dying, she begged her son to save her. Mon-El condemned his mother, having learned that she had killed his father.

Trivia

 * She was portrayed by Teri Hatcher, who also portrayed Lois Lane in Lois & Clark: The New Adventures of Superman". Hatcher also portrayed The Beldam from "Coraline".
 * They are both Dictators and Pure Evil.