His full name is Billy Kid (the inspiration is rather obvious), and he's a battle android, even if he'd rather be called an Intelligent Tactical Unit.
He's part of the off-jobs agency named Gentle House AKA Cunning Hare, and he basically looks like Vash the Stampede if he had mecha parts.
He's voiced in Japanese by Yu Hayashi (Issei Hoshino in the Judgment series, Ritsu in Octopath Traveler II, and Enra in Final Fantasy Type-0) while, as far as I can tell, the English voice actor still hasn't been announced officially albeit we do hear him in action in the trailer.
He's described as a "handsome cyborg with a casual and carefree personality" and he's certainly designed to be both cool and funny. He refers to himself as one of the Starlight Knights and he fights with two custom-made large-caliber revolvers who he calls "the girls."
He's said to be able to take on any challenge when he gets serious, despite the fact that he may look unreliable.
You can check out the trailer below in English, while you can find the Japanese version on the official YouTube channel, featuring Hoshino-san's voice. Incidentally, we also get a glimpse of two of his co-workers, his boss Nicole Demara and Anby Demara.
Update 11/22/2023: a second trailer has been released, featuring the first glimpse of Billy's gameplay. You can watch it below.
On top of the trailer featuring Billy, we also get the start date for the next closed beta tests, codenamed "Equalizing Test." It'll begin on November 24 at 11:00 a.m. UTC+8.
If you're unfamiliar with Zenless Zone Zero, it's an upcoming urban fantasy action RPG. It's going to be free-to-play with the inevitable microtransactions.
If you'd like to learn a lot more about the game, you can enjoy our interview with the producer from a couple of months ago and check out another trailer.