Sweet William Cigars act as the only type of legal drug Humans can abuse in Halo. Seriously its practically the only thing either than a dick that you see in a Marine's mouth. Its not like they have a choice. There's no other type of cigar or cigarette out there so they have to stick with these crimes against taste buds. They taste aweful despite their name. The name Sweet William was adopted when a guy named Ol' Willy took a smoke of it and died instantly. Upon dying a stream of feces pooled up around him that smelled like cotton candy (another drug that adds a sweet scent to your crap). Thus Sweet William became the name.