Belius was a captain of the Slane Theocracy knights that invaded Carne Village. He disguised himself as an imperial knight of the Baharuth Empire to lure out Gazef Stronoff into a trap set by the Sunlight Scripture.

He was described as an ordinary human with blonde hair and gray eyes. Belius was prone to anger and violence, but is a coward when his life is in danger.

The main reason he was able to join the knights of the Theocracy was because of the gold of his family, which was wealthy and owned many estates in the country. Although he was captain in name, he wasn't respected.

(Source: Overlord Wikia)