The Garthim are large clawed warriors of amazing strength on "The Dark Crystal" and they are the personal army of mechanical soldiers to the Skeksis.
The Garthim carried out the commands of SkekUng the Garthim-Master. The Garthim were created by SkekTek the scientist and lived in caverns beneath the Castle of the Crystal. The Garthim were dispatched to ravage Thra and returned with captive Gelfings or Podlings for the Skeksis to enslave and drain their essence. They act as the movie's secondary antagonists.
Physically, they resemble a cross between a beetle and a crab and don't appear to be 'alive' in the purest sense of the word: at the end of the Dark Crystal, they simply fall apart like suits of armor, revealing nothing within. It's possible they may be a form of robot, like a golem.