Nimue (Once Upon a Time)

"We're here. All of us, as promised, in the flesh.. and now it's time to get to work, to do what Dark Ones do best... snuff out the light."

- Nimue to Captain Hook Nimue is the true main antagonist in the first half of the fifth season of ABC's Once Upon a Time. She was the true love of Merlin, with whom she went on a quest with one day to make a sword out of the Holy Grail. However, during an encounter with Vortigan, the man who destroyed her town, Nimue kills him, having drank from the Grail, and becomes the first ever Dark One, now wearing Vortigan's mask as her own.

She is portrayed by Caroline Ford and Guy Fauchon (while masked).

She is apparently killed off by her successor and is sent to the Underworld for her evil. However, she is able to communicate from the Underworld through the mind of the current Dark One. When Emma Swan, the new Dark One, summons her, she mocks Emma for being nothing without Darkness. Emma rips the ember needed to complete Excalibur from her in response saying that she was never nothing. Nimue reminds Emma that she'll still be waiting in Emma's mind.

She persuades Captain Hook, who also became a Dark One after Emma used the sword to save his life, to sacrifice Merlin's heart to create a Dark Curse to return everyone to Storybrooke where Hook may have revenge on Rumplestiltskin.

In Storybrooke, she and the past Rumple appear from Emma's mind along with all other Dark Ones and watch her complete Excalibur.

Hook is taken by Darkness Rumple to the pond which has a connection to the Underworld, and he sinks his hook under the surface. The hook, covered in the blood of a former Dark One (Gold, although still alive) allows all Dark Ones, Nimue included, to return to the world of the living. Nimue, wearing her mask, leads the group and walks on the water's surface towards Hook, graciously accepting his hand and removing her mask. She tells Hook they must do what all Dark Ones were meant to do - snuff out the light. Hook welcomes her to Storybrooke as the Dark Ones descend upon the town, bringing the full power of the living Darkness with them.

Nimue is the main antagonist of the Winter Finale, "Swan Song". She marks each of the heroes with the mark of Charon, sacrificing their lives for the Dark Ones'. She blasts the heroes and teleports them to the lake, where all Dark Ones are gathered. When Emma tries to stop her and Hook, she attacks Emma and easily incapacitates her. Hook snaps out of his evil, saying that this is enough. He turns on Nimue. She smirks, saying he can't defeat her, but he responds that he can before using Excalibur on her, causing her to disintegrate slowly and be sucked into the sword as part of the Darkness, which Gold later takes back.