Zug is an ambitious, young tug who is Captain Zero's fourth tug, and one of the Z-Stack switchers. He is used for a wide variety of tasks around Bigg City Port. He speaks with a Midwest Estonian accent.
Zug mainly works with Zip, and likes to think of himself as the intelligent one. Compared to Zip, he certainly is intelligent and practical, but he is not as smart as the other tugs. He comes up with devious plans for him and Zip to use (although the plans usually fail). Despite being best friends with Zip, Zug basically commands him, who's too frightened to make any good suggestions.
Zug's capabilities range from the towing of barges to liner docking operations. Like the rest of the Zero Marine, he is based on the Moran Fleet tugs of the 1920's.
Zug is sneaky, cowardly and he needs the other Z-Stacks around for courage. Zug is a scheming sort of tug, though his plans rarely if ever work as planned. Zug is intimidated by the main Z-Stack Zorran and has a tendency to be somewhat nervous and jittery around him. However, as seen in Trapped, he did initially keep his cool while around Zorran, only to panic when Zorran's impatience landed the smaller tug in trouble.
Despite his scheming and troublesome schemes, as with Zebedee in High Winds, Zug is shown to have a good streak in him somewhere, which was the closest to be shown in Trapped after Zorran accidentally jammed a tramper across the river and callously abandoned Zug. As a result, Zug had been forced to work with the Star Fleet to get it out of the way since he was stuck on the other side, but he never complained. He was also shown to be very supportive with O.J.'s plan to ram it with a line of barges, despite it not working as expected; he even helped out in the attempt. This shows that even Zug is capable with working with the Star Tugs whenever something disastrous happens.
Zug and Zip are the Z-Stack equivalents of Ten Cents and Sunshine, in that they are the smaller tugs of the fleet, who work together and are plotting against the other two. Zug has major roles in most episodes, and a majority of stories focus on him as a major character in some way, usually concerning Zip.Zug's whistle has a hooting quality that sounds very much like a squeeze horn, but deeper.
- After Tugs' production ended, Zug's model was purchased by the Star Tugs Company, an organisation which aimed to restore and preserve the models.
- It is currently unknown if Zug's other face masks still remain in existence.
- In the Finnish version, Zug is called Suppala; sometimes he is just called Sisu.