William (Bill) S. Hammack (born 1961) is an American chemical engineer, and professor in the department of chemical engineering at the University of Illinois at Urbana–Champaign.
Hammack is well known for his ventures in science communication as the persona Engineer Guy: between 1999 and 2005 he produced radio commentaries for Illinois Public Media, and starting in 2010, he produced a regular series of videos on YouTube explaining the engineering of everyday objects. He is one of the authors of the book Eight Amazing Engineering Stories. He also authored the book The Things We Make: The Unknown History of Invention from Cathedrals to Soda Cans, as well as the book Fatal Flight: The True Story of Britain's Last Great Airship, which was also recorded as an audiobook read by the author.