Big Mac is Captain Star's second tug, who sports a distinctively broad Glaswegian accent. He is used for a variety of tasks around Bigg City Port. Usually, because he is one of the strongest tugs, it means he is supporting heavy loads. Big Mac is based on the tugs of San Francisco waters from the 1920s.
Big Mac can come across as a rude and stubborn tug, but he has a heart of gold, despite his tendencies to be gruff at times. He is very much willing to set aside his own safety for the sake of others, and usually remains level-headed when undergoing a strategy. Big Mac works mainly with his brother Warrior, and the two tugs have an extremely close friendship. Even though Warrior's clumsiness and thick head occasionally frustrate him, he still respects and cares for him. He also stands up for Warrior if anyone, especially the Z-Stacks, makes fun of him.As opposed to his gruff personality, he is fitted with a rich and melodic chime whistle.
Big Mac is an essential character to TUGS. He is the second strongest tug of the fleet and despite his sometimes abrasive manners, he can be kind and gentle. He is always willing to help out someone in trouble, and uses his great strength to help whenever he can. He also has a strong protective streak for the Star switchers, particularly if the Z-Stacks are mocking them.
Big Mac is painted in the Star Fleet's corporate livery. This consists of a black hull, a yellow superstructure, white mast and an American flag-styled red white and blue funnel. His name is painted on the sides of his bow in white and he has the number "2" on his funnel. He wears a navy blue cap.
- His name most likely derives from his Scottish heritage; it isn't to be confused and has nothing to do with McDonald's' popular burger of the same name (it is believed that his rename to Big Stack for Salty's Lighthouse was done to avoid a lawsuit from McDonald's since it is an American fast food chain and Salty's Ligthouse is also an American TV show).
- After Tugs' production ended, Big Mac's model was purchased by The Star Tugs Company, an organisation which aimed to restore and preserve the models.
- Although prior to his sale, he was so damaged that his hull had completely separated from the rest of his body, though he was repaired shortly before sale.
- He was only sold with his angry face mask, but he was reunited with his other face masks when the owner attended one of The Star Tugs Trust events at the Battlefield Line Railway in March 2014.