The Zeron Brotherhood are major antagonists in the Tales of Arcadia trilogy, serving as the central antagonists in Part 1 of 3Below, with the Zeron Alpha being a minor antagonist in Part 2.
They are a trio of bounty hunters sent by General Morando to kill Aja and Krel Tarron and crush the cores of King Fialkov and Queen Coranda. It is also revealed that he had them kill Varvatos Vex's family to make him vulnerable enough to lower the shields of Akiridion-5 and betray House Tarron so he could return to Akiridion-5 and dominate the planet.
At one point, the Zeron Brotherhood attempted to steal Gaylen's Core from the guard of House Tarron for unknown purposes. However, the King and Queen managed to stop them and give the core to the Trollhunter named Kanjigar the Courageous, hundreds of years ago, who kept it safe in a cavern he made, called "the Deep", where anyone who enters it faces their greatest fear.
It's also revealed that after General Morando was exiled from Akiridion-5 for high treason, he hired the Zeron Brotherhood to cause a massive bombing, thus killing Varvatos Vex's family and hundreds more Akiridions. Despite Varvatos begging King Fialkov to pursue the Brotherhood across the galaxy so he can satisfy his own veangeance, the latter refused as he was more interested in increasing the defenses of the planet. Following this, Morando ordered Varvatos to lower the shields while promising no one would be hurt upon his return, which he did upon being blinded by his anger.
Following his successful takeover of Akiridion-5, Morando hires the Zeron Brotherhood to be part of his bounty hunters across the galaxy to murder Aja and Krel Tarron and crush the life cores of their parents. Later, at the Intergalactic Way Station, they find out from a Foo-Foo the Royals' whereabouts, and slaughter everyone listening to them, and when they travel to Earth, they capture a Skelteg and use it to discover their location further.
Soon, Varvatos decides to confront them himself and gains the upper hand at first, but they prove to be too much for him. However, Aja arrives and helps him fight them off, while Krel sabotages their spaceship so they couldn't follow them.
After finding out that they cannot break through the Mothership's defensive barrier, the Zeron Brotherhood decides to wait for the Royals to be vulnerable enough to be attacked by them, which happens when Aja and Krel go to a bonfire, where Aja has her first date with Steve Palchuk. As Aja and Krel are being cornered by the Zeron Brotherhood, Varvatos arrives and kills Zeron Beta. Following this, Alpha and Omega express grief at his death.
Alpha and Omega eventually manage to capture Aja, Krel, and Steve inside their spaceship. During this time, Alpha threatens Varvatos that if he doesn't surrender the King and Queen's cores, then he will kill Aja and Krel. Because of this, Varvatos decides to trick them with fake royal cores that are actually bombs. When Alpha discovers that he was lied to, the bombs explode, and the spaceship plummets from the sky, and Steve finds out that Aja is an extraterrestrial. When they are both attacked by Omega, the spaceship crushes the latter.
While Alpha is mourning Omega's death. the first OMEN arrives to Earth, and Morando uses it to tell Alpha that since the Zeron Brotherhood failed in their task, he should submit to the OMEN if he wants to live. Alpha fearfully agrees to this.
Eventually, after Morgana creates the Eternal Night and sends Gunmar and the Gumm-Gumms to vanquish mankind, Alpha uses this time to track Aja and Krel to the Mothership and ambush them, where he harms Zadra. While the OMEN corrupts the Mothership's programming to make it leave Earth, Alpha keeps the Royals busy, but is knocked away by Buster. However, after Varvatos makes a sacrifice to crash the Mothership so the King and Queen's cores could remain safe from Morando and Merlin ends the Eternal Night, Alpha kidnaps Varvatos and takes his to the bounty hunters' outpost in the Moon, where he keeps him in confinement.
After the Royals rescue Varvatos from his prison, he goes on a one-on-one combat duel with Zeron Alpha outside the outpost. There, Alpha reveals that Morando sent him and his two comrades to orchestrate the tragic bombing that killed his family, specifically so that he would be convinced to lower the shields. Following this, Varvatos kills Alpha, thus avenging the deaths of his own family.