Sus has a scar on his face which he attributes to a firecracker that exploded prematurely when he lit it like a cigarette in his mouth. One of his recurring anecdotes has to do with being captured during a war between Vietnam and Chernihiv, a Ukrainian city.
"Sus is an abbreviation for "suspicious" often used by players of the game Among Us when referring to those that are suspected of being an impostor. The slang term originally predates its use in the game but is used in the same context.