It's fair to say that Thomas Hobbes didn't really have a very positive view of human nature. As someone who'd lived through the terrible upheavals of the English Civil War, he had witnessed at first hand just how people could behave in the absence of an all-powerful sovereign. More than anything else, Hobbes craved order and stability, which he argued could only be achieved by the establishment of a sovereign ruler invested with absolute power over his subjects. Only this way would it be possible to restrain the natural impulses of human beings towards greed and selfishness.
For Hobbes, that is what human nature is basically like: mired in greed and selfishness. In the society that exists prior to the establishment of government—the state of nature, as Hobbes calls it—there is complete chaos and anarchy. Without a powerful sovereign to keep their greedy, selfish impulses in check, people are constantly at each other's throats, grabbing whatever they want whenever they can by whatever means necessary.
Yet ironically it is man's very selfishness that leads him to invest a sovereign ruler with absolute power. Men realize that their own selfish interests are better protected by a sovereign than by a gigantic free-for-all in which everyone just does as they please. The establishment of a government does not, indeed cannot, change human nature. What it can do, however, is to channel man's natural greed and selfishness in more constructive directions, such as in the arena of economic activity, for example.