One major reason that people oppose the wto is because some believe that large companies will eventually rule the world

This is a false assumption and part of the general paranoia/conspiracy theories of the modern world.

In essence, the WTO or the World Trade Organization was developed to enhance global trade between different nations and maintain a set of rules, laws and agreements that can be mutually beneficial. 

More trade should be able to create more businesses, more jobs and eventually more economic prosperity for the participating countries.

Since, it does not always work out for everyone, a conspiracy theory involves, large corporations using WTO to 'control the world'.

Nothing can be further from the truth. The WTO is made up of elected/representative officials of all the countries.