There is no element as critical (as in criticality) to the development of nuclear power and nuclear weapons as uranium, and without uranium, neither would exist in their present forms. Also, the world would be a different place. Although it is not widely known, uranium has had many uses outside of nuclear applications, but the nuclear applications are (by far) the most important.
This paper is a review of all of the above, and also a review of a book from which I drew much of this information for this post.