Zetsk looks like a prehistoric man because of his height, build, and face.
Zetsk is very close to his brother Gashta, the only person he trusts. He has a violent character.
Greed Island arc
Zetsk with his brother Gashta take Tsezguerra's Ren test and the both of them pass the test with 7 other people. After entering the game Zetsk sits and waits for his brother Gashta in front of the Shiso Tree; sitting close by to Gon. Soon his brother walks down the stairs on the entrance and thanks him for waiting. Gashta then says they're being watched and Zetsk confirms it saying that they're several people spying on them and that they're not revealing themselves. Gashta however deduces they're no threat to them and since they could sense them from such a distance they should be ignored. The two brothers then head off further into the game.
The Bellam brothers are later mentioned by the Bombers that they're a duo they should keep an eye on. He and his brother are mentioned in Gon's binder and Goreinu says they're a famous duo who are very strong and never work with others. The brothers are later shown someplace in Greed Island listening to Eta give an announcement that a trivia game will then be held, with the prize for the game being the "Ruler's Blessing". After Gon wins the trivia game the brothers confront Gon and group. Gashta comments how Gon and group actually managed to get all of the cards in the game, while his brother Zetsk snickers. Zetsk then tells a man that apparently was associated with the brothers that his job is done and can go beat it and then challenges the group to a winner take all match and it doesn't matter if it's 2 versus 4. Gashta then tells the group it's a match they can't refuse, the brothers however are handily defeated, by the boys.
13th Hunter Chairman Election arc
Abilities & Powers
Zetsk is capable enough to have passed the notoriously difficult Hunter Exam. He is an above-average Greed Island player, praised as a capable individual by Goreinu and considered a troublesome opponent by Genthru despite only recently starting the game. His brother and he were feared by multiple players, although not as much as the Bombers. He is highly perceptive, having succeeded in sensing the presence of onlookers as soon as he joined the game, and making inferences about their species and skill level based on it. Nonetheless, Gashta and he were effortlessly defeated by Gon, Killua, Goreinu, and Biscuit.