fiction - Can I use real presidents (past and present) and real companies in a fictional story?

I'm not sure if I want to use real people and companies or make up an entirely different world with different people, presidents, and companies than our real world. If I did the latter I would offer the possibility of other universes in the preface and then use completely fictitious people. My main characters are of course fictitious, but they will be going on a journey to uncover hidden secrets from our nation's past and even from the world's past, so I need to know if these secrets they uncover can be about real people and companies (written in our real world) or if it would be better to make up companies and similar secrets to satisfy the story(written in an alternate universe).