From House of Hozz

the idea is a zombie that is in every encounter with zombies, so that we can track all zombie activity through thee proposed character tracking system.

it was probably created by zack.

I'm havin' a thought here. Ziggy The Zombie could be the Queen of the Undead, who Zack raises. He wanted to bring her back since he felt horrible about running her over. And really, where else would he find a fresh human corpse to make a zombie?