Zeg is a denizen of the underground world of Underzone. The worm surfaced on one occasion but found himself being harassed by a trio of bullies for being different. Zeg was rescued by Sonic the Hedgehog but accidentally led Miles "Tails" Prower to his secret home. As Tails was no longer allowed to leave, Zeg happily took Tails on a tour of his new home but was soon subjected to a direct spray of poison gas from a leak in the wall. Zeg survived and helped evacuate the area as Tails cleared up the spill. He then prevented any further danger by putting a cork in the gap.
At the bottom of the Underzone's hierarchy, Zeg is a miner who looks like all the other insignificant males. The only thing able to tell him apart from the others is that he doesn't wear a head-torch (although one panel shows that one of his colleagues has lost his lamp). It wasn't explained why Zeg ventured out to the Emerald Hill Zone. Being a worm, he probably enjoys eating mouldcake and smiled encouragingly at Tails when the fox was offered some.