Who is Evil-Lyn?
Evil-Lyn is Skeletor's second-in-command and also the only woman on the Evil Warriors' team.
She made her debut in 1983 as Mattel's attempt to add a woman on the bad guy's team to balance Teela whom (at the time) was the only woman on the good guys' team. And, just as Teela was a "Warrior Goddess" at that time, Evil-Lyn was labeled a Dark Goddess/Evil Goddess. Her body sculpt was exactly the same as Teela's but with a different head mold, and different color palette.
Was Evil-Lyn created as a love-interest for Skeletor?
No.
Originally, Evil-Lyn was created as a rival for Teela.
However, she very quickly became a love interest for Skeletor, as early as the newspaper comics published between 1983-85, Evil-Lyn decided that her endgame was to help Skeletor take over Eternia so that she could rule the world beside him as his queen.
This relationship continued on though the Filmation cartoon, the 200X reboot cartoon, the Classics-Line comics, and the Revelation series on Netflix.
[was gonna put an image of the making out on the throne scene from Rev., but I decided I didn't want to]
The only exceptions to this relationship were the New Adventures of He-Man, where Evil-Lyn doesn't appear at all; and the 2021 CGI Masters of the Universe series where Evil-Lyn appears to be shipped with Trap Jaw instead (although the ship does appear to be subtext).
What's Evil-Lyn's Backstory?
Evil-Lyn doesn't have one unified or consistent backstory.
One of Lyn's early concepts had her as an explorer from Earth whom crashed with Marlena, but while Marlena crashed near Eternos and was found by Randor, Lyn (as well as 2 others) were jettisoned and crashed in the Dark Lands instead where she was found by Skeletor and joined him.
[no image available]
This starkly different from her backstory in subsequent iterations of the franchise.
In the 200X reboot, Lyn's backstory has her as a Princess of a destroyed ancient civilization. When she was an infant, she was kidnapped by King Hiss and held as ransom against her father, the King of Zalesia. Her father did what Hiss wanted and Lyn was given back, but then Hiss destroyed Zalesia. As punishment her father was cursed with immortality and Lyn was taken by a time traveler into a future so that her father, now called the Faceless One, could raise her safely "away from the wars of Preternia". Sometime later, Lyn has left her father and is out on her own when she crosses paths with Keldor and his group who are trying to steal an artifact that she'd already stolen. After a brief scuffle and some cringe flirting, Lyn joins Keldor's group.
In the tie-in comics that pair with the Revelation series on Netflix, Lyn was being raised by a couple that may or may not have been her biological parents, but they turned out to be cannibals and tried to maim her to eat her limbs. She escapes them and flees into the sewers where she meets a witch, Magestra, who feeds her, raises her, and teaches her magic. Until Skeletor appears and gives Lyn a better offer.
The CGI series doesn't give a backstory for her (yet). But we do know that she's most likely from Eternia, she was a member of the royal court of King Randor before Keldor's coup, and -based off her accent- was probably born into a wealthy family that lived in the Upper Ward of the capital city.