Yull

Yull was Unggoy stationed on the Rapid Conversion and was part of Dadab's group. He was the first Covenant casualty of the Human-Covenant War. He killed Osmo by tearing his stomach apart, but then was killed by Tartarus, who pulled off his mask and threw him into a whirlpool and down a series of waterfalls.

Yull was less intelligent than average, as were most Unggoy on the ship.

Source

 * Halo: Contact Harvest