Challia Bull is a soldier in the Principality of Zeon's armed forces. Originally stationed on Jupiter, he returns to the Earth Sphere during the later stages of the One Year War. Upon return, he is summoned by Gihren Zabi, who believes that Bull is a Newtype and that his abilities could benefit Zeon. His Newtype abilities show through in their first meeting, as he can sense that he will be placed under Kycilia Zabi's command without Gihren needing to say a word.
Bull departs on the Dolos carrier and heads towards to Granada. Upon arrival, Kycilia assigns Bull to the MAN-03 Braw Bro with Lt. Simus Al Bakharov, but says that if he shows more Newtype ability than Lalah Sune, he may take over as pilot of the MAN-08 Elmeth. The Braw Bro then headed to Char Aznable's Zanzibar, where Bull meets Char and Lalah. In a futher display of his Newtype abilities, Bull is able to sense a strong pulse from Lalah. Char informs Bull that he believes the RX-78-2 Gundam pilot is a Newtype as well.
Bull takes the Braw Bro out, insisting that he merely wants to test it. He encounters the Gundam and engages it in battle; however, he was outclassed, and the battle would last a little under 10 minutes before the Braw Bro was destroyed and Bull was killed.