When first shown, he is wearing large plated armor with a personalized face guard in the shape of a male face complete with detailed nose, mouth, bone structure and eyes. His actual face is somewhat brutish with short, scraggly black hair. Without his armor on, he wears a white-sleeveless undershirt and dark pants with boots. After becoming an Apostle-Spawn, his appearance alters to show sharp, demonic teeth and snake-like eyes in addition to the multiple changes his body goes through as Guts damages him.
These changes include multiple growths that sprout out from wherever Guts attacks him, completely replacing two arms and even the Spawn itself sprouts out the side of Zondark's face to reveal it's groteqsue appearance, similar to the main body of the Count.
Zondark shows up with a very overconfident personality, much like any larger enemy that Guts faces in the series. He talks a big game when he first meets Guts, but surveys him with a bit of tactical intelligence involving Guts' weaponry. He also seems to enjoy a challenge, pitting his Warhammer vs. Guts' Dragonslayer in a test to see how it will fair in combat. When Guts does not seem to do anything more than defend, his confidence has an even higher boost and he proclaims that it doesn't matter the size of a weapon if the man wielding it hasn't the strength to do anything. Guts, replying with his blade, destroys the Warhammer and Zondark's mask forcing of metal into his eyes and face. Guts proceeds by standing on his face, pushing in the pieces while smirking he agrees with the statement that Zondark said, before making his escape with Vargas.
Zondark grows a massive grudge after this point, so much that it clouds his entire psyche with rage and he even kills an innocent doctor in the process. He's practically lost the ability to be reasoned with that is, until the Count arrives. It appears that Zondark fears his master, calming down after he's put into a headlock in fear of his own life. When asked if he could get his chance at slaying the Black Swordsman, he agrees without worrying of the consequences a hasty decision that costs him his humanity.
In his Apostle-Form, his personality is still present despite the fact that his body is mostly a puppet for the Count. He's primarily a mindless, rampaging tyrant at this point who will stop at nothing to kill Guts and his personality almost completely disappears after his head is slightly severed to reveal the growth inside.