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In 852 BCE, when the Sangheili joined the San'Shyuum to form the Covenant, Muskem was one of the many Sangheili that opposed the new alliance. When he heard about Ussa 'Xellus's rebellion against the Covenant the following year, he served as one of Ussa's informants. He told Ussa that there was numerous Sangheili that worked in Creck's geological energy plants and mines that were disgruntled with their living conditions and the Covenant. Ussa and his mate, Sooln, headed to Creck to meet with Muskem and recruit new members into their rebellion at the mines. However, the day before Ussa arrived at the planet, Muskem had allegedly fallen into a boiling pit of magma in the mines, where he was instantly incinerated. After speaking with Muskem's supervising officer, Ussa believed that someone had set up the "accident". Despite this, before his death, Muskem arranged for 'Crecka, under the name Quillick to meet with Ussa and Sooln, allowing 'Crecka to lead them to the Refuge.
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