Hiruko (ヒルコ) was once a great shinobi of Sunagakure. However, once he died, he became one of Sasori’s first Human Puppets and one of his favorites. As a puppet, he served as Sasori’s “puppet armor” as he could hide inside of him. Sasori even adorned Hiruko with the Akatsuki’s robes, and hid inside it so often that others came to recognize him only when he was wearing it.

Chiyo stated that Hiruko had changed since she saw him twenty years ago. After all of his strikes failed due to Chiyo’s manipulation, Haruno Sakura destroyed the puppet.

(Source: Narutopedia)