Helga Katrina Sinclair

"Commander, there were not supposed to be people down here. This changes everything."

- Helga discussing about the Atlantean natives. "Nothing personal."

- Helga's last words as she fires a flare at Rourke's balloon in revenge for his treachery.

Helga Katrina Sinclair is the hidden secondary antagonist (later anti-hero) of Disney's 41st full-length animated feature film, Atlantis: The Lost Empire. She is the former right-hand of Commander Lyle Tiberius Rourke.

She was voiced by Claudia Christian.

Role
Helga first appeared in the apartment of Milo James Thatch (the protagonist of the film), where she introduces herself to him and announced that her employer Preston Whitmore (who is a close friend of Milo's grandfather Thaddeus) is funding an expedition to find the lost city of Atlantis and that he wants Milo to be a part of. Sensing this as a opportunity to prove his claims about Atlantis true, Milo accepts the proposition.

During the journey, Helga is seen aiding her boss and the team into successfully locating the lost city (thanks to Milo's deciphering of the Atlantean language); she even took note to see how happy Milo is after finding the lost city. However, it turns out that Helga herself is aware of the existence of a powerful crystal called the Heart of Atlantis and that she and Rourke are planning to steal it to make themselves rich. Despite her greedy nature, Helga shows some remorse when she discovered they were going to steal from an ancient yet living civilization and showed some concern over it, though this did not stop her from going along with the plan.

During the final battle, Helga uses his pistol to shoot back against the heroes, but Milo crashes his flying stone fish into the blimp, causing it to descend further. To lighten the load on the balloon, Rourke betrays Helga by attempting to throw her off, but she glides back and beats him up, berating Rourke for his treachery. However, Rourke grabs her foot and successfully throws her out, where she hits the base of the volcano.

Using the last of her strength, Helga manages to fire a flare gun at the blimp before she dies, causing the blimp to descend further. This allows Milo to defeat Rourke by crystallizing and shredding him to pieces with the blimp's propellers and return the crystal to save Atlantis from an imminent volcanic explosion.

In the end, the crew return back to the surface while Milo stays behind in Atlantis to help rebuild its former glory, and they (along with Mr. Whitmore) form a cover story to keep the existence of Atlantis as a secret, describing Helga's fate as that she went missing in action, though Cookie almost spilled the beans on Helga's true circumstances before Mrs. Packard silences him.

Trivia

 * She is similar to Fidget from The Great Mouse Detective, both being thrown overboard to "lighten the load". However, unlike Fidget, Helga didn't back down until she was thrown overboard again, and was shown to still be alive for a little after the fall.
 * She is similar to May Day from A View to a Kill; both serve as right-hand women to their bosses (Rourke and Max Zorin), who subsequently betray them for their greed. The betrayals also led the women to sacrifice themselves to defeat their bosses in their plots (Helga shooting down Rourke's blimp to prevent him from escaping before dying, and May Day sacrificing herself to foil Zorin's scheme of destroying Silicon Valley).
 * Though she chose to accompany Rourke when he left with the Heart Of Atlantis, she had second thoughts about stealing from Atlantis when it became apparent that the Atlanteans were not extinct and that their city was still thriving. This, along with Rourke's betrayal, has led to several fan theories that Helga changed her ways and joined the Atlanteans during the film's climax. Some even go so far as to suggest that she not only survived her fall from the balloonbut was pardoned by and joined the Atlantean society. The Disney Wiki even states this in the article for the character, though there is no canonical evidence for this.