Sergeant Hobo 678 is the leader of Zim's training session on Hobo 13. He is a one-shot antagonist on Invader Zim.
Before the trainees can go on the course, Sergeant Hobo 678 says that the team needs a leader, and Zim votes himself and wins. To his disgust, Zim would go on to get all his team mates eliminated.
Hobo 678 then fought Zim. At first he had the upper hand until Zim siphoned the energy from Sergeant's suit to his, granting Zim the power to knock him out of the ring and win. Sergeant Hobo 678 and Skoodge were soon attacked by the dreaded Hogulus. Despite being angered by Zim's treating of his teammates the Sergeant grabbed Skoodge and bashed him against the Hogulus in an attempt to get the beast to open its mouth and free him. He was never heard from again following this.
- Sergeant Hobo 678 is voiced by the legendary R. Lee Ermey, a former drill sergeant famous for his role as Gunnery Sergeant Hartman in the film Full Metal Jacket. Since then, he has spent much of his acting career playing similar characters, many of them parodies of his "hard-edged drill sergeant" image.