Treblor, also known as "Buzzard", worked as an agent of the Zombarian Retrieval Department, and initially allied himself with Agents J and K to hunt down the interstellar criminal Z-Ron. However, when certain revelations were made, Treblor turned against the Men in Black agents. He has reappeared on Earth since then, now in his true character as a bounty hunter and mercenary.
He first came to earth pursuing an interstellar criminal named Z-Ron. Upon encountering Agents J and K, he introduces himself as a member of the Zombarian Retrieval Department, an interstellar law-enforcement group. He promptly presents official-looking arrival clearance papers, as well as a warrant for Z-Ron's arrest. Despite Agent J's concerns about Treblor "stealing [their] collar," Agent K proposes making the hunt for Z-Ron a joint operation, to which Treblor agrees.
After sharing information about Z-Ron and his crimes, Treblor accompanies the MiB agents. As they begin searching a nearby forest, Treblor suggests that they split up to cover more ground. K agrees, and sends J to "scout ahead" while K remains with Treblor. As they continue the search, K makes what seems like small talk, asking Treblor how long he has been with the Zombarian Retrieval Department, whom he has worked with, etc. When Treblor's answers don't add up, K calls L and Zed, who has the Twins run a background check on Treblor.
As it turns out, Treblor did work for the Zombarian Retrieval Department, but only very briefly. He now goes by the codename "Buzzard" - bounty hunter, mercenary, and "professional psycho". When K confronts him, Buzzard shoots him with a Vaculator - a device which spews 8,000-degree molten lava, and definitely not the sort of thing a cop would carry. Though K survives by freezing the lava blast with his Icer, he is trapped inside a cocoon of rock. Before he can activate his phone to warn J, Buzzard manages to find the younger agent, who has already caught Z-Ron, and tricks J into letting him take possession of the criminal.
Before Buzzard can escape with his quarry, however, J finds and frees K, and the two agents catch up to him before he reaches his ship. At first, Buzzard focuses on shooting Agent J, believing K to have been killed. When K attacks, J makes a break for it, carrying Z-Ron away while K and Buzzard shoot it out with each other using a variety of exotic alien weapons.
After a brief standoff, Buzzard and K shoot one another with Demolecularizer XL-12's, each destroying the other's weapon and knocking their opponent out. Buzzard seems to recover first, and quickly locates Z-Ron. Just as he is about to capture his prize, Agents J and L arrive. J grabs Buzzer's own stun weapon and hurls it at Z-Ron, who is paralyzed when it attaches to and shocks him. Agent K then reappears, informing Buzzard that "you're coming with us". It seems K was busy after he knocked Buzzard out - not only has he summoned a large force of MiB agents, but when Buzzard tries to flee in his ship, he finds out the hard way that K managed to plant a small explosive device on board. At the end of the episode, Buzzard's smoking ship is seen sailing out-of-control through space, and K predicts that "he'll probably just float around up there for ... oh, forever."
He later returned to Earth, attacking an underground MiB bullet train on which Agent J and a young Symbiote called Troy are traveling. Using a small explosive device, he derails the train, then pursues J and Troy above ground. At first, they are able to evade him, using Troy's abilities to shape-shift and enhance parts of Jay's body. Buzzard's current employer - who first appears as a floating metal sphere - is most displeased.
After a lengthy chase, Buzzard and the sphere catch up to J and Troy. A fight ensues, but this time, the sphere uses an energy beam to hold Jay in place, allowing Buzzard to draw an energy blade and cut Troy away from Jay's neck. As J and Troy are reeling from the sudden separation, the metal sphere lands, opening up to reveal Buzzard's employer: a small, elderly-looking alien, who intends to use the Symbiote's healing and strengthening powers for his own gain. As the client forces the young Symbiote to meld with his decrepit body, Buzzard asks to collect his fee - only to be interrupted by Agent K's appearance. Despite being initially weakened by the effects of an alien virus, K swiftly recovers, shooting Buzzard as Troy turns the client's body against him. Using Buzzard's own energy blade, K separates Troy from his abductor.
Since we last see Buzzard being shot by K, and nobody seems concerned about pursuing or transporting him, the simplest conclusion is that Buzzard was shot and killed at the scene. However, nobody seems concerned about calling in a clean-up crew for his remains, either, so it is also possible that he was simply stunned by the blast, and either slipped away or was taken into custody offscreen.
A version of Buzzard also appears in Jay's Vermax-induced dream. Apparently, he is trying to leave Earth in a spacecraft made from the Statue of Liberty's head. To capture him, Agent J, Agent L, and a dream version of Agent K somehow teleport onto the flying head, getting the drop on Buzzard as he sits obliviously in the cockpit, reading a newspaper. Dream-K tries to shoot Buzzard with a Noisy Cricket, but only blasts himself off the ship, plummeting to the ground far below (he later reappears by dropping through the ceiling of MiB headquarters, declaring "I'm okay!"). Thus, it is J who grabs Buzzard, lifts him up with one hand, then uses his ridiculous Kung Fu skills (emphasis on "ridiculous") to grab Buzzard's ankle and throw him around. We immediately jump to a scene in which Zed is shaking J's hand, congratulating him and declaring "he's like a son to me". Following typical dream-logic, the fate of the statue-head spaceship is never addressed.