the beast zazie

The most enigmatic member of the Gung-Ho Guns, Zazie's depiction varies significantly between the anime and manga.
In the anime, Zazie assumes the identity of a young boy named "Beeb" as a disguise. He wields control over sand-worms through a high-frequency device worn on his head.
The anime leaves Zazie's true nature ambiguous. It's speculated that he could be a malevolent entity taking over the boy when needed, an older man appearing youthful, or a child assassin driven to madness by his association with the Guns.
Manga:

Zazie's body is governed by a collective of hive-minded insects. These creatures are native inhabitants of Gunsmoke and have allied with Knives to determine whether humans or Plants make better cohabitants. The insects constituting Zazie also seem to embody the planet's consciousness, exemplified by his ability to command sandworms (Zazie has been dubbed the "leader of the sandworms" by Knives). His form is obliterated by Hoppered for spying on him and Midvalley. Later, Zazie reemerges in the body of a teenage girl. In Trigun Maximum 11, this vessel is also destroyed after attempting to implant an insect into Knives to control him. Zazie makes a final appearance as a peculiar-looking man in disco attire to deliver his coin to Vash. It's revealed these bodies are human but controlled by a small worm-like organism inside them, akin to what Zazie tried to insert into Knives. When the hive is annihilated by Knives, the man expels the creature and loses all memories of hosting Zazie.
His Gung-Ho Gun number is 12 in the manga and four in the anime.
(Source: Wikipedia, edited)