"The work concerns the structure of society and legitimate government, and is regarded as one of the earliest and most influential examples of social contract theory. Written during the English Civil War (1642–1651), it argues for a social contract and rule by an absolute sovereign. Hobbes wrote that civil war and the brute situation of a state of nature ("the war of all against all") could be avoided only by strong, undivided government."
The fact that this is the most assigned book at the "elite" institutions, and these are the people that end up in positions of corporate and government power, is troubling because of the philosophy that comes from this and what they feel they should do as power holders. Not to say this work isn't taught critically in universities or having some counterpoints elsewhere on this list, but it is still clearly influential and very much the way power is wielded.
(Edit: for context, I read Leviathan at one of those universities as a student. It is still a bedrock of political philosophy.)
(Edit 2: and no, please don't take this comment as some argument for "small government," it is not that at all)