Lieutenant Helga Katrina Sinclair is the secondary antagonist of Atlantis: The Lost Empire.
She was voiced by Claudia Christian.
She works for Lyle T. Rourke. Like Rouke, she does not appear to be initially evil until she has chosen to reveal it. Though she may seem like a cold, heartless mercenary like her boss, Helga is a really calculating, dangerous and mysterious woman who can handle herself and her cohorts in any situation. She helps Rourke find the crystal that keeps the Atlantians alive, helps him try and steal it, and finally tries to help Rourke fight off the heroes. Rourke, however, betrays Helga after she exclaims, "That's it, unless someone wants to jump!", meaning she can't lighten the load on Rourke's balloon. He tries to throw her off of his balloon to die so as to lighten the load. Helga tries to beat up Rourke in revenge, but he overpowers her and throws her off the balloon and she falls from a great height. Rourke mockingly apologizes to Helga, yelling, "Nothing personal!" Helga's fall supposedly kills her in almost the same way Professor Ratigan threw Fidget off his blimp from a height in The Great Mouse Detective.
- In the film, Helga wears green trousers and brown boots. In one of the posters and images of the film, her pants were goldish-yellow and her boots were lighter-brown, but in one of the storybooks, Helga's trousers were brown and she wears a yellow coat she did, but in the film, her coat was yellowish-white.
- Despite being listed as enemies, Helga and Audrey interact one point in the movie.
- One of the storybooks shows Helga resting after shooting the balloon with her flare gun. This scene didn't appear in the movie.
- Before Rourke punches Milo, Helga is not seen until she calls him to get ready.